AUTOGENOUS SOLDERING AND WELDING.--The b_Acetylene, the Principles of Its Generation and Use A Practical Handbook on the Production, Purification, and Subsequent Treatment of Acetylene for the Development of Light, Heat, and Power

welding and for the autogenous soldering or "burning" of wrought or cast

iron, steel, or copper. An apparatus consuming from 600 to 1000 litres of

acetylene per hour yields a flame whose inner zone is 10 to 15

millimetres long, and 3 to 4 millimetres in diameter; it is sufficiently

powerful to burn iron sheets 8 to 9 millimetres thick. By increasing the

supply of acetylene in proportion to that of the oxygen, the tip of the

inner zone becomes strongly luminous, and the flame then tends to

carburise iron; when the gases are so adjusted that this tip just

disappears, the flame is at its best for heating iron and steel. The

consumption of acetylene is about 75 litres per hour for each millimetre

of thickness in the sheet treated, and the normal consumption of oxygen

is 1.7 times as much; a joint 6 metres long can be burnt in 1 millimetre

plate per hour, and one of 1.5 metres in 10 millimetre plate. In certain

cases it is found economical to raise the metal to dull redness by other

means, say with a portable forge of the usual description, or with a

blowpipe consuming coal-gas and air. There are other forms of low-

pressure blowpipe besides the Fouché, in some of which the oxygen also is

supplied at low pressure. Apart from the use of cylinders of dissolved

acetylene, which are extremely convenient and practically indispensable

when the blowpipe has to be applied in confined spaces (as in repairing

propeller shafts on ships _in situ_), acetylene generators are now

made by several firms in a convenient transportable form for providing

the gas for use in welding or autogenous soldering. It is generally

supposed that the metal used as solder in soldering iron or steel by this

method must be iron containing only a trifling proportion of carbon (such

as Swedish iron), because the carbon of the acetylene carburises the

metal, which is heated in the oxy-acetylene flame, and would thereby make

ordinary steel too rich in carbon. But the extent to which the metal used

is carburised in the flame depends, as has already been indicated, on the

proper adjustment of the proportion of oxygen to acetylene. Oxy-acetylene

autogenous soldering or welding is applicable to a great variety of work,

among which may be mentioned repairs to shafts, locomotive frames,

cylinders, and to joints in ships' frames, pipes, boilers, and rails. The

use of the process is rapidly extending in engineering works generally.

Generators for acetylene soldering or welding must be of ample size to

meet the quickly fluctuating demands on them and must be provided with

water-seals, and a washer or scrubber and filter capable of arresting all

impurities held mechanically in the crude gas, and with a safety vent-

pipe terminating in the open at a distance from the work in hand. The

generator must be of a type which affords as little after-generation as

possible, and should not need recharging while the blowpipe is in use.

There should be a main tap on the pipe between the generator and the

blowpipe. It does not appear conclusively established that the gas

consumed should have been chemically purified, but a purifier of ample

size and charged with efficient material is undoubtedly beneficial. The

blowpipe must be designed so that it remains sufficiently cool to prevent

polymerisation of the acetylene and deposition of the resultant particles

of carbon or soot within it.

It is important to remember that if a diluent gas, such as nitrogen, is

present, the superior calorific power of acetylene over nearly all gases

should avail to keep the temperature of the flame more nearly up to the

temperature at which hydrogen and oxygen cease to combine. Hence a

blowpipe fed with air and acetylene would give a higher temperature than

any ordinary (atmospheric) coal-gas blowpipe, just as, as has been

explained in Chapter VI., an ordinary acetylene flame has a higher

temperature than a coal-gas flame. It is likely that a blowpipe fed with

"Lindé-air" (oxygen diluted with less nitrogen than in the atmosphere)

and acetylene would give as high a limelight effect as the oxy-hydrogen

or oxy-coal-gas blowpipe.

CHAPTER X

CARBURETTED ACETYLENE

Now that atmospheric or Bunsen burners for the consumption of acetylene

for use in lighting by the incandescent system and in heating have been

so much improved that they seem to be within measurable reach of a state

of perfection, there appears to be but little use at the present time for

a modified or diluted acetylene which formerly seemed likely to be

valuable for heating and certain other purposes. Nevertheless, the facts

relating to this so-called carburetted acetylene are in no way traversed

by its failure to establish itself as an active competitor with simple

acetylene for heating purposes, and since it is conceivable that the

advantages which from the theoretical standpoint the carburetted gas

undoubtedly possesses in certain directions may ultimately lead to its

practical utilisation for special purposes, it has been deemed expedient

to continue to give in this work an account of the principles underlying

the production and application of carburetted acetylene.

It has already been explained that acetylene is comparatively a less

efficient heating agent than it is an illuminating material, because, per

unit of volume, its calorific power is not so much greater than that of

coal-gas as is its illuminating capacity. It has also been shown that the

high upper explosive limit of mixtures of acetylene and air--a limit so

much higher than the corresponding figure with coal-gas and other gaseous

fuels--renders its employment in atmospheric burners (either for lighting

or for heating) somewhat troublesome, or dependent upon considerable

skill in the design of the apparatus. If, therefore, either the upper

explosive limit of acetylene could be reduced, or its calorific value

increased (or both), by mixing with it some other gas or vapour which

should not seriously affect its price and convenience as a self-luminous

illuminant, acetylene would compare more favourably with coal-gas in its

ready applicability to the most various purposes. Such a method has been

suggested by Heil, and has been found successful on the Continent. It

consists in adding to the acetylene a certain proportion of the vapour of

a volatile hydrocarbon, so as to prepare what is called "carburetted

acetylene." In all respects the method of making carburetted acetylene is

identical with that of making "air-gas," which was outlined in Chapter

I., viz., the acetylene coming from an ordinary generating plant is led

over or through a mass of petroleum spirit, or other similar product, in

a vessel which exposes the proper amount of superficial area to the

passing gas. In all respects save one the character of the product is

similar to that of air-gas, _i.e._, it is a mixture of a permanent

gas with a vapour; the vapour may possibly condense in part within the

mains if they are exposed to a falling temperature, and if the product is

to be led any considerable distance, deposition of liquid may occur

(conceivably followed by blockage of the mains) unless the proportion of

vapour added to the gas is kept below a point governed by local climatic

and similar conditions. But in one most important respect carburetted

acetylene is totally different from air-gas: partial precipitation of

spirit from air-gas removes more or less of the solitary useful

constituent of the material, reducing its practical value, and causing

the residue to approach or overpass its lower explosive limit (_cf._

Chapter I.); partial removal of spirit from carburetted acetylene only

means a partial reconversion of the material into ordinary acetylene,

increasing its natural illuminating power, lowering its calorific

intensity somewhat, and causing the residue to have almost its primary

high upper explosive limit, but essentially leaving its lower explosive

limit unchanged. Thus while air-gas may conceivably become inefficient

for every purpose if supplied from any distance in very cold weather, and

may even pass into a dangerous explosive within the mains; carburetted

acetylene can never become explosive, can only lose part of its special

heating value, and will actually increase in illuminating power.

It is manifest that, like air-gas, carburetted acetylene is of somewhat

indefinite composition, for the proportion of vapour, and the chemical

nature of that vapour, may vary. 100 litres of acetylene will take up 40

grammes of petroleum spirit to yield 110 litres of carburetted acetylene

evidently containing 9 per cent. of vapour, or 100 litres of acetylene

may be made to absorb as much as 250 grammes of spirit yielding 200

litres of carburetted acetylene containing 50 per cent. of vapour; while

the petroleum spirit may be replaced, if prices are suitable, by benzol

or denatured alcohol.

The illuminating power of acetylene carburetted with petroleum spirit has

been examined by Caro, whose average figures, worked out in British

units, are:

ILLUMINATING POWER OF CARBURETTED ACETYLENE.

HALF-FOOT BURNERS.

_Self-luminous._ | _Incandescent_

1 litre = 1.00 candle. | 1 litre = 3.04 candles.

1 cubic foot = 28.4 candles. | 1 cubic foot = 86.2 candles.

1 candle = 1.00 litre. | 1 candle = 0.33 litre.

1 candle = 0.035 cubic foot. | 1 candle = 0.012 cubic foot.

Those results may be compared with those referring to air-gas, which

emits in incandescent burners from 3.0 to 12.4 candles per cubic foot

according to the amount of spirit added to the air and the temperature to

which the gas is exposed.

The calorific values of carburetted acetylene (Caro), and those of other

gaseous fuels are:

Large Calories per

_ Cubic Foot.

| (Lewes) . 320

| (Gand) . 403

Ordinary acetylene . . | (Heil) . 365

| ___

|_Mean . . 363

| Maximum . 680

Carburetted acetylene . . | Minimum . 467

(petroleum spirit) | ___

|_Mean . . 573

Carburetted acetylene (50 per cent. benzol by volume) 685

Carburetted acetylene (50 per cent. alcohol by volume) 364

Coal-gas (common, unenriched) . . . . . 150

| Maximum . 178

Air-gas, self-luminous flame | Minimum . 57

| ___

|_Mean . . . 114

| Maximum . 26

Air-gas, non-luminous flame | Minimum . 18

| ___

|_Mean . . . 22

Water-gas (Strache) from coke . . . . . 71

Mond gas (from bituminous coal) . . . . . 38

Semi-water-gas from coke or anthracite . . . 36

Generator (producer) gas . . . . . . 29

Besides its relatively low upper explosive limit, carburetted acetylene

exhibits a higher temperature of ignition than ordinary acetylene, which

makes it appreciably safer in presence of a naked light. It also

possesses a somewhat lower flame temperature and a slower speed of

propagation of the explosive wave when mixed with air. These data are:

______________________________________________________________________

| | | | |

| |_____________|__________________| Wave. |

|________________________|______|______|________|_________|____________|

| | | | | | |

| Acetylene (theoretical)| --- | --- | --- |1850-2420| --- |

| " (observed) | 3.35 | 52.3 | 480 |1630-2020| 0.18-100 |

| Carburetted \ from | 2.5 | 10.2 | 582 | 1620 | 3.2 |

| acetylene / . . to | 5.4 | 30.0 | 720 | 1730 | 5.3 |

| Carburetted acetylene\ | 3.4 | 22.0 | --- | 1820 | 1.3 |

| Carburetted acetylene\ | 3.1 | 12.0 | --- | 1610 | 1.1 |

| Air-gas, self-luminous\|15.0 | 50.0 | --- |1510-1520| --- |

| Coal-gas . . . | 7.9 | 19.1 | 600 | --- | --- |

|________________________|______|______|________|_________|____________|

In making carburetted acetylene, the pressure given by the ordinary

acetylene generator will be sufficient to drive the gas through the

carburettor, and therefore there will be no expense involved beyond the

cost of the spirit vaporised. Thus comparisons may fairly be made between

ordinary and carburetted acetylene on the basis of material only, the

expense of generating the original acetylene being also ignored. In Great

Britain the prices of calcium carbide, petroleum spirit, and 90s benzol

delivered in bulk in country places may be taken at 15£ per ton, and

1s. per gallon respectively, petroleum spirit having a specific

gravity of 0.700 and benzol of 0.88. On this basis, a unit volume (100

cubic metres) of plain acetylene costs 1135d., of "petrolised"

acetylene containing 66 per cent. of acetylene costs 1277d., and

of "benzolised" acetylene costs 1180d. In other words, 100 volumes

of plain acetylene, 90 volumes of petrolised acetylene, and 96 volumes of

benzolised acetylene are of equal pecuniary value. Employing the data

given in previous tables, it appears that 38.5 candles can be won from

plain acetylene in a self-luminous burner, and 103 candles therefrom in

an incandescent burner at the same price as 25.5-29.1 and 78-87 candles

can be obtained from carburetted acetylene; whence it follows that at

English prices petrolised acetylene is more expensive as an illuminant in

either system of combustion than the simple gas, while benzolised

acetylene, burnt under the mantle only, is more nearly equal to the

simple gas from a pecuniary aspect. But considering the calorific value,

it appears that for a given sum of money only 363 calories can be

obtained from plain acetylene, while petrolised acetylene yields 516, and

benzolised acetylene 658; so that for all heating or cooking purposes

(and also for driving small motors) carburetted acetylene exhibits a

notable economy. Inasmuch as the partial saturation of acetylene with any

combustible vapour is an operation of extreme simplicity, requiring no

power or supervision beyond the occasional recharging of the carburettor,

it is manifest that the original main coming from the generator supplying

any large establishment where much warming, cooking (or motor driving)

might conveniently be done with the gas could be divided within the

plant-house, one branch supplying all, or nearly all, the lighting

burners with plain acetylene, and the other branch communicating with a

carburettor, so that all, or nearly all, the warming and cooking stoves

(and the motor) should be supplied with the more economical carburetted

acetylene. Since any water pump or similar apparatus would be in an

outhouse or basement, and the most important heating stove (the cooker)

be in the kitchen, such an arrangement would be neither complicated nor

involve a costly duplication of pipes.

It follows from the fact that even a trifling proportion of vapour

reduces the upper limit of explosibility of mixtures of acetylene with

air, that the gas may be so lightly carburetted as not appreciably to

suffer in illuminating power when consumed in self-luminous jets, and yet

to burn satisfactorily in incandescent burners, even if it has been

generated in an apparatus which introduces some air every time the

operation of recharging is performed. To carry out this idea, Caro has

suggested that 5 kilos. of petroleum spirit should be added to the

generator water for every 50 cubic metres of gas evolved, _i.e._, 1

lb. per 160 cubic feet, or, say, 1 gallon per 1000 cubic feet, or per 200

lb. of carbide decomposed. Caro proposed this addition in the case of

central installations supplying a district where the majority of the

consumers burnt the gas in self-luminous jets, but where a few preferred

the incandescent system; but it is clearly equally suitable for

employment in all private plants of sufficient magnitude.

A lowering of the upper limit of explosibility is also produced by the

presence of the acetone which remains in acetylene when obtained from a

cylinder holding the compressed gas (_cf._ Chapter XI.). According

to Wolff and Caro such gas usually carries with it from 30 to 60 grammes

of acetone vapour per cubic metre, _i.e._, 1.27 grammes per cubic

foot on an average; and this amount reduces the upper limit of

explosibility by about 16 per cent., so that to this extent the gas

behaves more smoothly in an incandescent burner of imperfect design.

Lépinay has described some experiments on the comparative technical value

of ordinary acetylene, carburetted acetylene, denatured alcohol and

petroleum spirit as fuels for small explosion engines. One particular

motor of 3 (French) h.p. consumed 1150 grammes of petroleum spirit per

hour at full load; but when it was supplied with carburetted acetylene

its consumption fell to 150 litres of acetylene and 700 grammes of spirit

(specific gravity 0.680). A 1-1/4 h.p. engine running light required 48

grammes of 90 per cent. alcohol per horse-power-hour and 66 litres of

acetylene; at full load it took 220 grammes of alcohol and 110 litres of

acetylene. A 6 h.p. engine at full load required 62 litres of acetylene

carburetted with 197 grammes of petroleum spirit per horse-power-hour

(uncorrected); while a similar motor fed with low-grade Taylor fuel-gas

took 1260 litres per horse-power-hour, but on an average developed the

same amount of power from 73 litres when 10 per cent. of acetylene was

added to the gas. Lépinay found that with pure acetylene ignition of the

charge was apt to be premature; and that while the consumption of

carburetted acetylene in small motors still materially exceeded the

theoretical, further economics could be attained, which, coupled with the

smooth and regular running of an engine fed with the carburetted gas,

made carburetted acetylene distinctly the better power-gas of the two.

CHAPTER XI

COMPRESSED AND DISSOLVED ACETYLENE--MIXTURES WITH OTHER GASES

In all that was said in Chapters II., III., IV., and V. respecting the

generation and employment of acetylene, it was assumed that the gas would

be produced by the interaction of calcium carbide and water, either by

the consumer himself, or in some central station delivering the acetylene

throughout a neighbourhood in mains. But there are other methods of using

the gas, which have now to be considered.

COMPRESSED ACETYLENE.--In the first place, like all other gases,

acetylene is capable of compression, or even of conversion into the

liquid state; for as a gas, the volume occupied by any given weight of it

is not fixed, but varies inversely with the pressure under which it is

stored. A steel cylinder, for instance, which is of such size as to hold

a cubic foot of water, also holds a cubic foot of acetylene at

atmospheric pressure, but holds 2 cubic feet if the gas is pumped into it

to a pressure of 2 atmospheres, or 30 lb. per square inch; while by

increasing the pressure to 21.53 atmospheres at 0° C. (Ansdell, Willson

and Suckert) the gas is liquefied, and the vessel may then contain 1

cubic foot of liquid acetylene, which is equal to some 400 cubic feet of

gaseous acetylene at normal pressure. It is clear that for many purposes

acetylene so compressed or liquefied would be convenient, for if the

cylinders could be procured ready charged, all troubles incidental to

generation would be avoided. The method, however, is not practically

permissible; because, as pointed out in Chapters II. and VI., acetylene

does not safely bear compression to a point exceeding 2 atmospheres; and

the liability to spontaneous dissociation or explosion in presence of

spark or severe blow, which is characteristic of compressed gaseous

acetylene, is greatly enhanced if compression has been pushed to the

point of liquefaction.

However, two methods of retaining the portability and convenience of

compressed acetylene with complete safety have been discovered. In one,

due to the researches of Claude and Hess, the gas is pumped under

pressure into acetone, a combustible organic liquid of high solvent

power, which boils at 56° C. As the solvent capacity of most liquids for

most gases rises with the pressure, a bottle partly filled with acetone

may be charged with acetylene at considerable effective pressure until

the vessel contains much more than its normal quantity of gas; and when

the valve is opened the surplus escapes, ready for employment, leaving

the acetone practically unaltered in composition or quantity, and fit to

receive a fresh charge of gas. In comparison with liquefied acetylene,

its solution in acetone under pressure is much safer; but since the

acetone expands during absorption of gas, the bottle cannot be entirely

filled with liquid, and therefore either at first, or during consumption

(or both), above the level of the relatively safe solution, the cylinder

contains a certain quantity of gaseous acetylene, which is compressed

above its limit of safety. The other method consists in pumping acetylene

under pressure into a cylinder apparently quite full of some highly

porous solid matter, like charcoal, kieselguhr, unglazed brick, &c. This

has the practical result that the gas is held under a high state of

compression, or possibly as a liquid, in the minute crevices of the

material, which are almost of insensible magnitude; or it may be regarded

as stored in vessels whose diameter is less than that in which an

explosive wave can be propagated (_cf._ Chapter VI.).

DISSOLVED ACETYLENE.--According to Fouché, the simple solution of

acetylene in acetone has the same coefficient of expansion by heat as

that of pure acetone, viz., 0.0015; the corresponding coefficient of

liquefied acetylene is 0.007 (Fouché), or 0.00489 (Ansdell) _i.e._,

three or five times as much. The specific gravity of liquid acetylene is

0.420 at 16.4° C. (Ansdell), or 0.528 at 20.6° C. (Willson and Suckert);

while the density of acetylene dissolved in acetone is 0.71 at 15° C.

(Claude). The tension of liquefied acetylene is 21.53 atmospheres at 0°

C., and 39.76 atmospheres at 20.15° C. (Ansdell); 21.53 at 0° C., and

39.76 at 19.5° C. (Willson and Suckert); or 26.5 at 0° C., and 42.8 at

20.0° C. (Villard). Averaging those results, it may be said that the

tension rises from 23.2 atmospheres at 0° C. to 40.77 at 20° C., which is

an increment of 1/26 or 0.88 atmosphere, per 1° Centigrade; while, of

course, liquefied acetylene cannot be kept at all at a temperature of 0°

unless the pressure is 21 atmospheres or upwards. The solution of

acetylene in acetone can be stored at any pressure above or below that of

the atmosphere, and the extent to which the pressure will rise as the

temperature increases depends on the original pressure. Berthelot and

Vieille have shown that when (_a_) 301 grammes of acetone are

charged with 69 grammes of acetylene, a pressure of 6.74 atmospheres at

14.0° C. rises to 10.55 atmospheres at 35.7° C.; (_b_) 315 grammes

of acetone are charged with 118 grammes of acetylene, a pressure of 12.25

atmospheres at 14.0° C. rises to 19.46 at 36.0° C.; (_c_) 315

grammes of acetone are charged with 203 grammes of acetylene, a pressure

of 19.98 atmospheres at 13.0° C. rises to 30.49 at 36.0° C. Therefore in

(_a_) the increase in pressure is 0.18 atmosphere, in (_b_)

O.33 atmosphere, and in (_c_) 0.46 atmosphere per 1° Centigrade

within the temperature limits quoted. Taking case (_b_) as the

normal, it follows that the increment in pressure per 1° C. is 1/37

(usually quoted as 1/30); so that, measured as a proportion of the

existing pressure, the pressure in a closed vessel containing a solution

of acetylene in acetone increases nearly as much (though distinctly less)

for a given rise in temperature as does the pressure in a similar vessel

filled with liquefied acetylene, but the absolute increase is roughly

only one-third with the solution as with the liquid, because the initial

pressure under which the solution is stored is only one-half, or less,

that at which the liquefied gas must exist.

Supposing, now, that acetylene contained in a closed vessel, either as

compressed gas, as a solution in acetone, or as a liquid, were brought to

explosion by spark or shock, the effects capable of production have to be

considered. Berthelot and Vieille have shown that if gaseous acetylene is

stored at a pressure of 11.23 kilogrammes per square centimetre,

[Footnote: 1 kilo. per sq. cm. is almost identical with 1 atmosphere, or

15 lb. per sq. inch.] the pressure after explosion reaches 92.33

atmospheres on an average, which is an increase of 8.37 times the

original figure; if the gas is stored at 21.13 atmospheres, the mean

pressure after explosion is 213.15 atmospheres, or 10.13 times the

original amount. If liquid acetylene is tested similarly, the original

pressure, which must clearly be more than 21.53 atmospheres (Ansdell) at

0° C., may rise to 5564 kilos, per square centimetre, as Berthelot and

Vieille observed when a steel bomb having a capacity of 49 c.c. was

charged with 18 grammes of liquefied acetylene. In the case of the

solution in acetone, the magnitudes of the pressures set up are of two

entirely different orders according as the original pressure 20

atmospheres or somewhat less; but apart from this, they vary considerably

with the extent to which the vessel is filled with the liquid, and they

also depend on whether the explosion is produced in the solution or in

the gas space above. Taking the lower original pressure first, viz., 10

atmospheres, when a vessel was filled with solution to 33 per cent. of

its capacity, the pressure after explosion reached about 95 atmospheres

if the spark was applied to the gas space; but attained 117.4 atmospheres

when the spark was applied to the acetone. When the vessel was filled 56

per cent. full, the pressures after explosion reached about 89, or 155

atmospheres, according as the gas or the liquid was treated with the

spark. But when the original pressure was 20 atmospheres, and the vessel

was filled to 35 per cent. of its actual capacity with solution, the

final pressures ranged from 303 to 568 atmospheres when the gas was

fired, and from 2000 to 5100 when the spark was applied to the acetone.

Examining these figures carefully, it will be seen that the phenomena

accompanying the explosion of a solution of acetylene in acetone resemble

those of the explosion of compressed gaseous acetylene when the original

pressure under which the solution is stored is about 10 atmospheres; but

resemble those of the explosion of liquefied acetylene when the original

pressure of the solution reaches 20 atmospheres, this being due to the

fact that at an original pressure of 10 atmospheres the acetone itself

does not explode, but, being exothermic, rather tends to decrease the

severity of the explosion; whereas at an original pressure of 20

atmospheres the acetone does explode (or burn), and adds its heat of

combustion to the heat evolved by the acetylene. Thus at 10 atmospheres

the presence of the acetone is a source of safety; but at 20 atmospheres

it becomes an extra danger.

Since sound steel cylinders may easily be constructed to boar a pressure

of 250 atmospheres, but would be burst by a pressure considerably less

than 5000 atmospheres, it appears that liquefied acetylene and its

solution in acetone at a pressure of 20 atmospheres are quite unsafe; and

it might also seem that both the solution at a pressure of 10 atmospheres

and the simple gas compressed to the same limit should be safe. But there

is an important difference here, in degree if not in kind, because, given

a cylinder of known capacity containing (1) gaseous acetylene compressed

to 10 atmospheres, or (2) containing the solution at the same pressure,

if an explosion were to occur, in case (1) the whole contents would

participate in the decomposition, whereas in case (2), as mentioned

already, only the small quantity of gaseous acetylene above the solution

would be dissociated.

It is manifest that of the three varieties of compressed acetylene now

under consideration, the solution in acetone is the only one fit for

general employment; but it exhibits the grave defects (_a_) that the

pressure under which it is prepared must be so small that the pressure in

the cylinders can never approach 20 atmospheres in the hottest weather or

in the hottest situation to which they may be exposed, (_b_) that

the gas does not escape smoothly enough to be convenient from large

vessels unless those vessels are agitated, and (_c_) that the

cylinders must always be used in a certain position with the valve at the

top, lest part of the liquid should run out into the pipes. For these

reasons the simple solution of acetylene in acetone has not become of

industrial importance; but the processes of absorbing either the gas, or

better still its solution in acetone, in porous matter have already

achieved considerable success. Both methods have proved perfectly safe

and trustworthy; but the combination of the acetone process with the

porous matter makes the cylinders smaller per unit volume of acetylene

they contain. Several varieties of solid matter appear to work

satisfactorily, the only essential feature in their composition being

that they shall possess a proper amount of porosity and be perfectly free

from action upon the acetylene or the acetone (if present). Lime does

attack acetone in time, and therefore it is not a suitable ingredient of

the solid substance whenever acetylene is to be compressed in conjunction

with the solvent; so that at present either a light brick earth which has

a specific gravity of 0.5 is employed, or a mixture of charcoal with

certain inorganic salts which has a density of 0.3, and can be introduced

through a small aperture into the cylinder in a semi-fluid condition.

Both materials possess a porosity of 80 per cent., that is to say, when a

cylinder is apparently filled quite full, only 20 per cent, of the space

is really occupied by the solid body, the remaining 80 per cent, being

available for holding the liquid or the compressed gas. If all

comparisons as to degree of explosibility and effects of explosion are

omitted, an analogy may be drawn between liquefied acetylene or its

compressed solution in acetone and nitroglycerin, while the gas or

solution of the gas absorbed in porous matter resembles dynamite.

Nitroglycerin is almost too treacherous a material to handle, but as an

explosive (which in reason absorbed or dissolved acetylene is not)

dynamite is safe, and even requires special arrangements to explode it.

In Paris, where the acetone process first found employment on a large

scale, the company supplying portable cylinders to consumers uses large

storage vessels filled, as above mentioned, apparently full of porous

solid matter, and also charged to about 43 per cent, of their capacity

with acetone, thus leaving about 37 per cent. of the apace for the

expansion which occurs as the liquid takes up the gas. Acetylene is

generated, purified, and thoroughly dried according to the usual methods;

and it is then run through a double-action pump which compresses it first

to a pressure of 3.5 kilos., next to a pressure of 3.5 x 3.5 = 12 kilos,

per square centimetre, and finally drives it into the storage vessels.

Compression is effected in two stages, because the process is accompanied

by an evolution of much heat, which might cause the gas to explode during

the operation; but since the pump is fitted with two cylinders, the

acetylene can be cooled after the first compression. The storage vessels

then contain 100 times their apparent volume of acetylene; for as the

solubility of acetylene in acetone at ordinary temperature and pressure

is about 25 volumes of gas in 1 of liquid, a vessel holding 100 volumes

when empty takes up 25 x 43 = 1000 volumes of acetylene roughly at

atmospheric pressure; which, as the pressure is approximately 10

atmospheres, becomes 1000 x 10 = 10,000 volumes per 100 normal capacity,

or 100 times the capacity of the vessel in terms of water. From these

large vessels, portable cylinders of various useful dimensions, similarly

loaded with porous matter and acetone, are charged simply by placing them

in mutual contact, thus allowing the pressure and the surplus gas to

enter the small one; a process which has the advantage of renewing the

small quantity of acetone vaporised from the consumers' cylinders as the

acetylene is burnt (for acetone is somewhat volatile, cf. Chapter X.), so

that only the storage vessels ever need to have fresh solvent introduced.

Where it is procurable, the use of acetylene compressed in this fashion

is simplicity itself; for the cylinders have only to be connected with

the house service-pipes through a reducing valve of ordinary

construction, set to give the pressure which the burners require. When

exhausted, the bottle is simply replaced by another. Manifestly, however,

the cost of compression, the interest on the value of the cylinders, and

the carriage, &c., make the compressed gas more expensive per unit of

volume (or light) than acetylene locally generated from carbide and

water; and indeed the value of the process does not lie so much in the

direction of domestic illumination as in that of the lighting, and

possibly driving, of vehicles and motor-cars--more especially in the

illumination of such vehicles as travel constantly, or for business

purposes, over rough road surfaces and perform mostly out-and-home

journeys. Nevertheless, absorbed acetylene may claim close attention for

one department of household illumination, viz., the portable table-lamp;

for the base of such an apparatus might easily be constructed to imitate

the acetone cylinder, and it could be charged by simple connexion with a

larger one at intervals. In this way the size of the lamp for a given

number of candle-hours would be reduced below that of any type of actual

generator, and the troubles of after-generation, always more or less

experienced in holderless generators, would be entirely done away with.

Dissolved acetylene is also very useful for acetylene welding or

autogenous soldering.

The advantages of compressed and absorbed acetylene depend on the small

bulk and weight of the apparatus per unit of light, on the fact that no

amount of agitation can affect the evolution of gas (as may happen with

an ordinary acetylene generator), on the absence of any liquid which may

freeze in winter, and on there being no need for skilled attention except

when the cylinders are being changed. These vessels weigh between 2.5 and

3 kilos, per 1 litre capacity (normal) and since they are charged with

100 times their apparent volume of acetylene, they may be said to weigh 1

kilo, per 33 litres of available acetylene, or roughly 2 lb. per cubic

foot, or, again, if half-foot burners are used, 2 lb. per 36 candle-

hours. According to Fouché, if electricity obtained from lead

accumulators is compared with acetylene on the basis of the weight of

apparatus needed to evolve a certain quantify of light, 1 kilo, of

acetylene cylinder is equal to 1.33 kilos, of lead accumulator with arc

lamps, or to 4 kilos. of accumulator with glow lamps; and moreover the

acetylene cylinder can be charged and discharged, broadly speaking, as

quickly or as slowly as may be desired; while, it may be added, the same

cylinder will serve one or more self-luminous jets, one or more

incandescent burners, any number and variety of heating apparatus,

simultaneously or consecutively, at any pressure which may be required.

From the aspect of space occupied, dissolved acetylene is not so

concentrated a source of artificial light as calcium carbide; for 1

volume of granulated carbide is capable of omitting as much light as 4

volumes of compressed gas; although, in practice, to the 1 volume of

carbide must be added that of the apparatus in which it is decomposed.

LIQUEFIED ACETYLENE.--In most civilised countries the importation,

manufacture, storage, and use of liquefied acetylene, or of the gas

compressed to more than a fraction of one effective atmosphere, is quite

properly prohibited by law. In Great Britain this has been done by an

Order in Council dated November 26, 1897, which specifies 100 inches of

water column as the maximum to which compression may be pushed. Power

being retained, however, to exempt from the order any method of

compressing acetylene that might be proved safe, the Home Secretary

issued a subsequent Order on March 28, 1898, permitting oil-gas

containing not more than 20 per cent, by volume of acetylene (see below)

to be compressed to a degree not exceeding 150 lb. per square inch,

_i.e._, to about 10 atmospheres, provided the gases are mixed

together before compression; while a third Order, dated April 10, 1901,

allows the compression of acetylene into cylinders filled as completely

as possible with porous matter, with or without the presence of acetone,

to a pressure not exceeding 150 lb. per square inch provided the

cylinders themselves have been tested by hydraulic pressure for at least

ten minutes to a pressure not less than double [Footnote: In France the

cylinders are tested to six times and in Russia to five times their

working pressure.] that which it is intended to use, provided the solid

substance is similar in every respect to the samples deposited at the

Home Office, provided its porosity does not exceed 80 per cent., provided

air is excluded from every part of the apparatus before the gas is

compressed, provided the quantity of acetone used (if used at all) is not

sufficient to fill the porosity of the solid, provided the temperature is

not permitted to rise during compression, and provided compression only

takes place in premises approved by H.M.'s Inspectors of Explosives.

DILUTED ACETYLENE.--Acetylene is naturally capable of admixture or

dilution with any other gas or vapour; and the operation may be regarded

in either of two ways; (1) as a, means of improving the burning qualities

of the acetylene itself, or (2) as a means of conferring upon some other

gas increased luminosity. In the early days of the acetylene industry,

generation was performed in so haphazard a fashion, purification so

generally omitted, and the burners were so inefficient, that it was

proposed to add to the gas a comparatively small proportion of some other

gaseous fluid which should be capable of making it burn without

deposition of carbon while not seriously impairing its latent

illuminating power. One of the first diluents suggested was carbon

dioxide (carbonic acid gas), because this gas is very easy and cheap to

prepare; and because it was stated that acetylene would bear an addition

of 5 or even 8 per cent, of carbon dioxide and yet develop its full

degree of luminosity. This last assertion requires substantiation; for it

is at least a grave theoretical error to add a non-inflammable gas to a

combustible one, as is seen in the lower efficiency of all flames when

burning in common air in comparison with that which they exhibit in

oxygen; while from the practical aspect, so harmful is carbon dioxide in

an illuminating gas, that coal-gas and carburetted water-gas are

frequently most rigorously freed from it, because a certain gain in

illuminating power may often thus be achieved more cheaply than by direct

enrichment of the gas by addition of hydrocarbons. Being prepared from

chalk and any cheap mineral acid, hydrochloric by preference, in the

cold, carbon dioxide is so cheap that its price in comparison with that

of acetylene is almost _nil_; and therefore, on the above

assumption, 105 volumes of diluted acetylene might be made essentially

for the same price as 100 volumes of neat acetylene, and according to

supposition emit 5 per cent. more light per unit of volume.

It is reported that several railway trains in Austria are regularly

lighted with acetylene containing 0.4 to 1.0 per cent. of carbon dioxide

in order to prevent deposition of carbon at the burners. The gas is

prepared according to a patent process which consists in adding a certain

proportion of a "carbonate" to the generator water. In the United

Kingdom, also, there are several installations supplying an acetylene

diluted with carbon dioxide, the gas being produced by putting into that

portion of a water-to-carbide generator which lies nearest to the water-

supply some solid carbonate like chalk, and using a dilute acid to attack

the material. Other inventors have proposed placing a solid acid, like

oxalic, in the former part of a generator and decomposing it with a

carbonate solution; or they have suggested putting into the generator a

mixture of a solid acid and a solid soluble carbonate, and decomposing it

with plain water.

Clearly, unless the apparatus in which such mixtures as these are

intended to be prepared is designed with considerable care, the amount of

carbon dioxide in the gas will be liable to vary, and may fall to zero.

If any quantity of carbide present has been decomposed in the ordinary

way, there will be free calcium hydroxide in the generator; and if the

carbon dioxide comes into contact with this, it will be absorbed, unless

sufficient acid is employed to convert the calcium carbonate (or

hydroxide) into the corresponding normal salt of calcium. Similarly,

during purification, a material containing any free lime would tend to

remove the carbon dioxide, as would any substance which became alkaline

by retaining the ammonia of the crude gas.

It cannot altogether be granted that the value of a process for diluting

acetylene with carbon dioxide has been established, except in so far as

the mere presence of the diluent may somewhat diminish the tendency of

the acetylene to polymerise as it passes through a hot burner (_cf._

Chapter VIII.). Certainly as a fuel-gas the mixture would be less

efficient, and the extra amount of carbon dioxide produced by each flame

is not wholly to be ignored. Moreover, since properly generated and

purified acetylene can be consumed in proper burners without trouble, all

reason for introducing carbon dioxide has disappeared.

MIXTURES OF ACETYLENE AND AIR.--A further proposal for diluting acetylene

was the addition to it of air. Apart from questions of explosibility,

this method has the advantage over that of adding carbon dioxide that the

air, though not inflammable, is, in virtue of its contained oxygen, a

supporter of combustion, and is required in a flame; whereas carbon

dioxide is not only not a supporter of combustion, but is actually a

product thereof, and correspondingly more objectionable. According to

some experiments carried out by Dufour, neat acetylene burnt under

certain conditions evolved between 1.0 and 1.8 candle-power per litre-

hour; a mixture of 1 volume of acetylene with 1 volume of air evolved 1.4

candle-power; a mixture of 1 volume of acetylene with 1.2 volumes of air,

2.25 candle-power; and a mixture of 1 volume of acetylene with 1.3

volumes of air, 2.70 candle-power per litre-hour of acetylene in the

several mixtures. Averaging the figures, and calculating into terms of

acetylene (only) burnt, Dufour found neat acetylene to develop 1.29

candle-power per litre-hour, and acetylene diluted with air to develop

1.51 candle-power. When, however, allowance is made for the cost and

trouble of preparing such mixtures the advantage of the process

disappears; and moreover it is accompanied by too grave risks, unless

conducted on a largo scale and under most highly skilled supervision, to

be fit for general employment.

Fouché, however, has since found the duty, per cubic foot of neat

acetylene consumed in a twin injector burner at the most advantageous

rate of 3.2 inches, to be as follows for mixtures with air in the

proportions stated:

Percentage of air 0 17 27 33.5

Candles per cubic feet 38.4 36.0 32.8 26.0

At lower pressures, the duty of the acetylene when diluted appears to be

relatively somewhat higher. Figures which have been published in regard

to a mixture of 30 volumes of air and 70 volumes of acetylene obtained by

a particular system of producing such a mixture, known as the "Molet-

Boistelle," indicate that the admixture of air causes a slight increase

in the illuminating duty obtained from the acetylene in burners of

various sizes. The type of burner and the pressure employed in these

experiments were not, however, stated. This system has been used at

certain stations on the "Midi" railway in France. Nevertheless even where

the admixture of air to acetylene is legally permissible, the risk of

obtaining a really dangerous product and the nebulous character of the

advantages attainable should preclude its adoption.

In Great Britain the manufacture, importation, storage, and use of

acetylene mixed with air or oxygen, in all proportions and at all

pressures, with or without the presence of other substances, is

prohibited by an Order in Council dated July 1900; to which prohibition

the mixture of acetylene and air that takes place in a burner or

contrivance in which the mixture is intended to be burnt, and the

admixture of air with acetylene that may unavoidably occur in the first

use or recharging of an apparatus (usually a water-to-carbide generator),

properly designed and constructed with a view to the production of pure

acetylene, are the solitary exceptions.

MIXED CARBIDES.--In fact the only processes for diluting acetylene which

possess real utility are that of adding vaporised petroleum spirit or

benzene to the gas, as was described in Chapter X. under the name of

carburetted acetylene, and one other possible method of obtaining a

diluted acetylene directly from the gas-generator, to which a few words

will now be devoted. [Footnote: Mixtures of acetylene with relatively

large proportions of other illuminating gases, such as are referred to on

subsequent pages, are also, from one aspect, forms of diluted acetylene.]

Calcium carbide is only one particular specimen of a large number of

similar metallic compounds, which can be prepared in the electric

furnace, or otherwise. Some of those carbides yield acetylene when

treated with water, some are not attacked, some give liquid products, and

some yield methane, or mixtures of methane and hydrogen. Among the latter

is manganese carbide. If, then, a mixture of manganese carbide and

calcium carbide is put into an ordinary acetylene generator, the gas

evolved will be a mixture of acetylene with methane and hydrogen in

proportions depending upon the composition of the carbide mixture. It is

clear that a suitable mixture of the carbides might be made by preparing

them separately and bulking the whole in the desired proportions; while

since manganese carbide can be won in the electric furnace, it might be

feasible to charge into such a furnace a mixture of lime, coke, and

manganese oxide calculated to yield a simple mixture of the carbides or a

kind of double carbide. Following the lines which have been adopted in

writing the present book, it is not proposed to discuss the possibility

of making mixed carbides; but it may be said in brief that Brame and

Lewes have carried out several experiments in this direction, using

charges of lime and coke containing (_a_) up to 20 per cent. of

manganese oxide, and (_b_) more than 60 per cent. of manganese

oxide. In neither case did they succeed in obtaining a material which

gave a mixture of acetylene and methane when treated with water; in case

(_a_) they found the gas to be practically pure acetylene, so that

the carbide must have been calcium carbide only; in case (_b_) the

gas was mainly methane and hydrogen, so that the carbide must have been

essentially that of manganese alone. Mixed charges containing between 20

and 60 per cent. of manganese oxide remain to be studied; but whether

they would give mixed carbides or no, it would be perfectly simple to mix

ready-made carbides of calcium and manganese together, if any demand for

a diluted acetylene should arise on a sufficiently large scale. It is,

however, somewhat difficult to appreciate the benefits to be obtained

from forms of diluted acetylene other than those to which reference is

made later in this chapter.

There is, nevertheless, one modification of calcium carbide which, in a

small but important sphere, finds a useful _rôle_. It has been

pointed out that a carbide containing much calcium phosphide is usually

objectionable, because the gas evolved from it requires extra

purification, and because there is the (somewhat unlikely) possibility

that the acetylene obtained from such material before purification may be

spontaneously inflammable. If, now, to the usual furnace charge of lime

and coke a sufficient quantity of calcium phosphate is purposely added,

it is possible to win a mixture of calcium phosphide and carbide, or, as

Bradley, Read, and Jacobs call it, a "carbophosphide of calcium," having

the formula Ca_5C_6P_2, which yields a spontaneously inflammable mixture

of acetylene, gaseous phosphine, and liquid phosphine when treated with

water, and which, therefore, automatically gives a flame when brought

into contact with the liquid. The value of this material will be

described in Chapter XIII.

GAS-ENRICHING.--Other methods of diluting acetylene consist in adding a

comparatively small proportion of it to some other gas, and may be

considered rather as processes for enriching that other gas with

acetylene. Provided the second gas is well chosen, such mixtures exhibit

properties which render them peculiarly valuable for special purposes.

They have, usually, a far lower upper limit of explosibility than that of

neat acetylene, and they admit of safe compression to an extent greatly

exceeding that of acetylene itself, while they do not lose illuminating

power on compression. The second characteristic is most important, and

depends on the phenomena of "partial pressure," which have been referred

to in Chapter VI. When a single gas is stored at atmospheric pressure, it

is insensibly withstanding on all sides and in all directions a pressure

of roughly 15 lb. per square inch, which is the weight of the atmosphere

at sea-level; and when a mixture of two gases, X and Y, in equal volumes

is similarly stored it, regarded as an entity, is also supporting a

pressure of 15 lb. per square inch. But in every 1 volume of that mixture

there is only half a volume of X and Y each; and, ignoring the presence

of its partner, each half-volume is evenly distributed throughout a space

of 1 volume. But since the volume of a gas stands in inverse ratio to the

pressure under which it is stored, the half-volume of X in the 1 volume

of X + Y apparently stands at a pressure of half an atmosphere, for it

has expanded till it fills, from a chemical and physical aspect, the

space of 1 volume: suitable tests proving that it exhibits the properties

which a gas stored at a pressure of half an atmosphere should do.

Therefore, in the mixture under consideration, X and Y are both said to

be at a "partial pressure" of half an atmosphere, which is manifestly 7.5

lb. per square inch. Clearly, when a gas is an entity (either an element

or one single chemical compound) partial and total pressure are

identical. Now, it has been shown that acetylene ceases to be a safe gas

to handle when it is stored at a pressure of 2 atmospheres; but the limit

of safety really occurs when the gas is stored at a _partial_

pressure of 2 atmospheres. Neat acetylene, accordingly, cannot be

compressed above the mark 30 lb. shown on a pressure gauge; but diluted

acetylene (if the diluent is suitable) may be compressed in safety till

the partial pressure of the acetylene itself reaches 2 atmospheres. For

instance, a mixture of equal volumes of X and Y (X being acetylene)

contains X at a partial pressure of half the total pressure, and may

therefore be compressed to (2 / 1/2 =) 4 atmospheres before X reaches the

partial pressure of 2 atmospheres; and therewith the mixture is brought

just to the limit of safety, any effect of Y one way or the other being

neglected. Similarly, a mixture of 1 volume of acetylene with 4 volumes

of Y may be safely compressed to a pressure of (2 / 1/5 =) 10

atmospheres, or, broadly, a mixture in which the percentage of acetylene

is _x_ may be safely compressed to a pressure not exceeding (2 /

_x_/100) atmospheres. This fact permits acetylene after proper

dilution to be compressed in the same fashion as is allowable in the case

of the dissolved and absorbed gas described above.

If the latent illuminating power of acetylene is not to be wasted, the

diluent must not be selected without thought. Acetylene burns with a very

hot flame, the luminosity of which is seriously decreased if the

temperature is lowered. As mentioned in Chapter VIII., this may be done

by allowing too much air to enter the flame; but it may also be effected

to a certain extent by mixing with the acetylene before combustion some

combustible gas or vapour which burns at a lower temperature than

acetylene itself. Manifestly, therefore, the ideal diluent for acetylene

is a substance which possesses as high a flame temperature as acetylene

and a certain degree of intrinsic illuminating power, while the lower the

flame temperature of the diluent and the less its intrinsic illuminating

power, the less efficiently will the acetylene act as an enriching

material. According to Love, Hempel, Wedding, and others, if acetylene is

mixed with coal-gas in amounts up to 8 per cent. or thereabouts, the

illuminating power of the mixture increases about 1 candle for every 1

per cent. of acetylene present: a fact which is usually expressed by

saying that with coal-gas the enrichment value of acetylene is 1 candle

per 1 per cent. Above 8 per cent., the enrichment value of acetylene

rises, Love having found an increase in illuminating power, for each 1

per cent. of acetylene in the mixture, of 1.42 candles with 11.28 per

cent. of acetylene; and of 1.54 candles with 17.62 per cent. of

acetylene. Theoretically, if the illuminating power of acetylene is taken

at 240 candles, its enrichment value should be (240 / 100 =) 2.4 candles

per 1 per cent.; and since, in the case of coal-gas, its actual

enrichment value falls seriously below this figure, it is clear that

coal-gas is not an economical diluent for it. Moreover, coal-gas can be

enriched by other methods much more cheaply than with acetylene. Simple

("blue") water-gas, according to Love, requires more than 10 per cent. of

acetylene to be added to it before a luminous flame is produced; while a

mixture of 20.3 per cent. of acetylene and 79.7 per cent. of water-gas

had an illuminating power of 15.47 candles. Every addition to the

proportion of acetylene when it amounted to 20 per cent. and upwards of

the mixture had a very appreciable effect on the illuminating power of

the latter. Thus with 27.84 per cent. of acetylene, the illuminating

power of the mixture was 40.87 candles; with 38.00 per cent. of acetylene

it was 73.96 candles. Acetylene would not be an economical agent to

employ in order to render water-gas an illuminating gas of about the

quality of coal-gas, but the economy of enrichment of water-gas by

acetylene increases rapidly with the degree of enrichment demanded of it.

Carburetted water-gas which, after compression under 16 atmospheres

pressure, had an illuminating power of about 17.5 candles, was enriched

by additions of acetylene. 4.5 per cent. of acetylene in the mixture gave

an illuminating power of 22.69 candles; 8.4 per cent., 29.54 candles;

11.21 per cent., 35.05 candles; 15.06 per cent., 42.19 candles; and 21.44

per cent., 52.61 candles. It is therefore evident that the effect of

additions of acetylene on the illuminating power of carburetted water-gas

is of the same order as its effect on coal-gas. The enrichment value of

the acetylene increases with its proportion in the mixture; but only when

the proportion becomes quite considerable, and, therefore, the gas of

high illuminating power, does enrichment by acetylene become economical.

Methane (marsh-gas), owing to its comparatively high flame temperature,

and to the fact that it has an intrinsic, if small, illuminating power,

is a better diluent of acetylene than carbon monoxide or hydrogen, in

that it preserves to a greater extent the illuminative value of the

acetylene.

Actually comparisons of the effect of additions of various proportions of

a richly illuminating gas, such as acetylene, on the illuminative value

of a gas which has little or no inherent illuminating power, are largely

vitiated by the want of any systematic method for arriving at the

representative illuminative value of any illuminating gas. A statement

that the illuminating power of a gas is _x_ candles is, strictly

speaking, incomplete, unless it is supplemented by the information that

the gas during testing was burnt (1) in a specified type of burner, and

(2) either at a specified fixed rate of consumption or so as to afford a

light of a certain specified intensity. There is no general agreement,

even in respect of the statutory testing of the illuminating power of

coal-gas supplies, as to the observance of uniform conditions of burning

of the gas under test, and in regard to more highly illuminating gases

there is even greater diversity of conditions. Hence figures such as

those quoted above for the enrichment value of acetylene inevitably show

a certain want of harmony which is in reality due to the imperfection or

incompleteness of the modes of testing employed. Relatively to another,

one gas appears advantageously merely in virtue of the conditions of

assessing illuminating power having been more favourable to it. Therefore

enrichment values, such as those given, must always be regarded as only

approximately trustworthy in instituting comparisons between either

different diluent gases or different enriching agents.

ACETYLENE MIXTURES FOR RAILWAY-CARRIAGE LIGHTING.--In modern practice,

the gases which are most commonly employed for diluents of acetylene,

under the conditions now being considered, are cannel-coal gas (in

France) and oil-gas (elsewhere). Fowler has made a series of observations

on the illuminating value of mixtures of oil-gas and acetylene. 13.41 per

cent. of acetylene improved the illuminating power of oil-gas from 43 to

49 candles. Thirty-nine-candle-power oil-gas had its illuminating power

raised to about 60 candles by an admixture of 20 per cent. of acetylene,

to about 80 candles by 40 per cent. of acetylene, and to about 110

candles by 60 per cent. of acetylene. The difficulty of employing

mixtures fairly rich in acetylene, or pure acetylene, for railway-

carriage lighting, lies in the poor efficiency of the small burners which

yield from such rich gas a light of 15 to 20 candle-power, such as is

suitable for the purpose. For the lighting of railway carriages it is

seldom deemed necessary to have a flame of more than 20 candle-power, and

it is somewhat difficult to obtain such a flame from oil-gas mixtures

rich in acetylene, unless the illuminative value of the gas is wasted to

a considerable extent. According to Bunte, 15 volumes of coal-gas, 8

volumes of German oil-gas, and 1.5 volumes of acetylene all yield an

equal amount of light; from which it follows that 1 volume of acetylene

is equivalent to 5.3 volumes of German oil-gas.

A lengthy series of experiments upon the illuminating power of mixtures

of oil-gas and acetylene in proportions ranging between 10 and 50 per

cent. of the latter, consumed in different burners and at different

pressures, has been carried out by Borck, of the German State Railway

Department. The figures show that per unit of volume such mixtures may

give anything up to 6.75 times the light evolved by pure oil-gas; but

that the latent illuminating power of the acetylene is less

advantageously developed if too much of it is employed. As 20 per cent.

of acetylene is the highest proportion which may be legally added to oil-

gas in this country, Borck's results for that mixture may be studied:

______________________________________________________________________

| | | | | | | |

|___________|________|_______|__________|_________|__________|_________|

| | | | | | | |

| Bray | 00 | 42 | 82 | 56.2 | 1.15 | 3.38 |

| " | 000 | 35 | 54 | 28.3 | 1.91 | 4.92 |

| " | 0000 | 35 | 43.3 | 16 | 2.71 | 4.90 |

| burner | 15 | 24 | 21 | 7.25 | 2.89 | 4.53 |

| " " | 30 | 15 | 22 | 10.5 | 2.09 | 3.57 |

| " " | 40 | 16 | 33.5 | 20.2 | 1.65 | 3.01 |

| " " | 60 | 33 | 73 | 45.2 | 1.62 | 3.37 |

| |

| The oil-gas from which this mixture was prepared showing: |

| |

| Bray | 00 | 34 | 73.5 | 16.6 | 4.42 | ... |

| " | 000 | 30 | 48 | 6.89 | 6.96 | ... |

| " | 0000 | 28 | 39 | 3.26 | 11.6 | ... |

| burner | 15 | 21 | 19 | 1.6 | 11.8 | ... |

| " " | 30 | 14 | 21.5 | 2.94 | 7.31 | ... |

| " " | 40 | 15 | 33 | 6.7 | 4.92 | ... |

| " " | 60 | 25 | 60 | 13.4 | 4.40 | ... |

|___________|________|_______|__________|_________|__________|_________|

It will be seen that the original oil-gas, when compressed to 10

atmospheres, gave a light of 1 candle-hour for an average consumption of

7.66 litres in the Bray burners, and for a consumption of 7.11 litres in

the ordinary German oil-gas jets; while the mixture containing 20 per

cent. of acetylene evolved the same amount of light for a consumption of

2.02 litres in Bray burners, or of 2.06 litres in the oil-gas jets.

Again, taking No. 40 as the most popular and useful size of burner, 1

volume of acetylene oil-gas may be said to be equal to 3 volumes of

simple oil-gas, which is the value assigned to the mixture by the German

Government officials, who, at the prices ruling there, hold the mixture

to be twice as expensive as plain oil-gas per unit of volume, which means

that for a given outlay 50 per cent. more light may be obtained from

acetylene oil-gas than from oil-gas alone.

This comparison of cost is not applicable, as it stands, to compressed

oil-gas, with and without enrichment by acetylene, in this country, owing

to the oils from which oil-gas is made being much cheaper and of better

quality here than in Germany, where a heavy duty is imposed on imported

petroleum. Oil-gas as made from Scotch and other good quality gas-oil in

this country, usually has, after compression, an illuminating duty of

about 8 candles per cubic foot, which is about double that of the

compressed German oil-gas as examined by Borck.

Hence the following table, containing a summary of results obtained by H.

Fowler with compressed oil-gas, as used on English railways, must be

accepted rather than the foregoing, in so far as conditions prevailing in

this country are concerned. It likewise refers to a mixture of oil-gas

and acetylene containing 20 per cent. of acetylene.

______________________________________________________________________

| | | | | | |

|_____________|_________|___________|______|___________|_______________|

| | | | | | |

| Oil-gas . . | 0.7 | 0.98 | 12.5 | 12.72 | 1.65 |

| Bray 000 . | 0.7 | 1.17 | 14.4 | 12.30 | 1.57 |

| " 0000 . | 0.7 | 0.97 | 10.4 | 10.74 | 1.41 |

| " 00000 | 0.7 | 0.78 | 5.6 | 7.16 | 1.08 |

| " 000000 | 0.7 | 0.55 | 1.9 | 3.52 | 1.14 |

|_____________|_________|___________|______|___________|_______________|

[Footnote 1: Data relating to the relative pecuniary values of acetylene

(carburetted or not), coal-gas, paraffin, and electricity as heating or

illuminating agents, are frequently presented to British readers after

simple recalculation into English equivalents of the figures which obtain

in France and Germany. Such a method of procedure is utterly incorrect,

as it ignores the higher prices of coal, coal-gas, and especially

petroleum products on the Continent of Europe, which arise partly from

geographical, but mainly from political causes.]

The mixture was tried also at higher pressures in the same burners, but

with less favourable results in regard to the duty realised. The oil-gas

was also tried at various pressures, and the most favourable result is

taken for computing the ratio in the last column. It is evident from this

table that 1 volume of this acetylene-oil-gas mixture is equal at the

most to 1.65 volume of the simple oil-gas. Whether the mixture will prove

cheaper under particular conditions must depend on the relative prices of

gas-oil and calcium carbide at the works where the gas is made and

compressed. At the prevailing prices in most parts of Britain, simple

oil-gas is slightly cheaper, but an appreciable rise in the price of gas-

oil would render the mixture with acetylene the cheaper illuminant. The

fact remains, however, that per unit weight or volume of cylinder into

which the gas is compressed, acetylene oil-gas evolves a higher candle-

power, or the same candle-power for a longer period, than simple,

unenriched British oil-gas. Latterly, however, the incandescent mantle

has found application for railway-carriage lighting, and poorer

compressed gases have thereby been rendered available. Thus coal-gas, to

which a small proportion of acetylene has been added, may advantageously

displace the richer oil-gas and acetylene mixtures.

Patents have been taken out by Schwander for the preparation of a mixture

of acetylene, air, and vaporised petroleum spirit. A current of naturally

damp, or artificially moistened, air is led over or through a mass of

calcium carbide, whereby the moisture is replaced by an equivalent

quantity of acetylene; and this mixture of acetylene and air is

carburetted by passing it through a vessel of petroleum spirit in the

manner adopted with air-gas. No details as to the composition,

illuminating power, and calorific values of the gas so made have been

published. It would clearly tend to be of highly indefinite constitution

and might range between what would be virtually inferior carburetted

acetylene, and a low-grade air-gas. It is also doubtful whether the

combustion of such gas would not be accompanied by too grave risks to

render the process useful.

CHAPTER XII

SUNDRY USES

There are sundry uses for acetylene, and to some extent for carbide,

which are not included in what has been said in previous chapters of this

book; and to them a few words may be devoted.

In orchards and market gardens enormous damage is frequently done to the

crops by the ravages of caterpillars of numerous species. These

caterpillars cannot be caught by hand, and hitherto it has proved

exceedingly difficult to cope with them. However, when they have changed

into the perfect state, the corresponding butterflies and moths, like

most other winged insects, are strongly attracted by a bright light. As

acetylene can easily be burnt in a portable apparatus, and as the burners

can be supplied with gas at such comparatively high pressure that the

flames are capable of withstanding sharp gusts of wind even when not

protected by glass, the brilliant light given by acetylene forms an

excellent method of destroying the insects before they have had time to

lay their eggs. Two methods of using the light have been tried with

astonishing success: in one a naked flame is supported within some

receptacle, such as a barrel with one end knocked out, the interior of

which is painted heavily with treacle; in the other the flame is

supported over an open dish filled with some cheap heavy oil (or perhaps

treacle would do equally well). In the first case the insects are

attracted by the light and are caught by the adhesive surfaces; in the

second they are attracted and singed, and then drowned in, or caught by,

the liquid. Either a well-made, powerful, vehicular lamp with its bull's-

eye (if any) removed could be used for this purpose, or a portable

generator of any kind might be connected with the burner through a

flexible tube. It is necessary that the lights should be lit just before

dusk when the weather is fine and the nights dark, and for some twenty

evenings in June or July, exactly at the period of the year when the

perfect insects are coming into existence. In some of the vineyards of

Beaujolais, in France, where great havoc has been wrought by the pyralid,

a set of 10-candle-power lamps were put up during July 1901, at distances

of 150 yards apart, using generators containing 6 oz. of carbide, and

dishes filled with water and petroleum 18 or 20 inches in diameter. In

eighteen nights, some twenty lamps being employed, the total catch of

insects was 170,000, or an average of 3200 per lamp per night. At French

prices, the cost is reported to have been 8 centimes per night, or 32

centimes per hectare (2.5 acres). In Germany, where school children are

occasionally paid for destroying noxious moths, two acetylene lamps

burning for twelve evenings succeeded in catching twice as many insects

as the whole juvenile population of a village during August 1902. A

similar process has been recommended for the destruction of the malarial

mosquito, and should prove of great service to mankind in infected

districts. The superiority of acetylene in respect of brilliancy and

portability will at once suggest its employment as the illuminant in the

"light" moth-traps which entomologists use for entrapping moths. In these

traps, the insects, attracted by the light, flutter down panes of glass,

so inclined that ultimate escape is improbable; while they are protected

from injury through contact with the flame by moans of an intervening

sheet of glass.

Methods of spraying with carbide dust have been found useful in treating

mildew in vines; while a process of burying small quantities of carbide

at the roots has proved highly efficacious in exterminating phylloxera in

the French and Spanish vineyards. It was originally believed that the

impurities of the slowly formed acetylene, the phosphine in particular,

acted as toxic agents upon the phylloxera; and therefore carbide

containing an extra amount of decomposable phosphides was specially

manufactured for the vine-growers. But more recently it has been argued,

with some show of reason, that the acetylene itself plays a part in the

process, the effects produced being said to be too great to be ascribed

wholly to the phosphine. It is well known that many hydrocarbon vapours,

such as the vapour of benzene or of naphthalene, have a highly toxic

action on low organisms, and the destructive effect of acetylene on

phylloxera may be akin to this action.

As gaseous acetylene will bear a certain amount of pressure in safety--a

pressure falling somewhat short of one effective atmosphere--and as

pressure naturally rises in a generating apparatus where calcium carbide

reacts with water, it becomes possible to use this pressure as a source

of energy for several purposes. The pressure of the gas may, in fact, be

employed either to force a stream of liquid through a pipe, or to propel

certain mechanism. An apparatus has been constructed in France on the

lines of some portable fire-extinguishing appliances in which the

pressure set up by the evolution of acetylene in a closed space produces

a spray of water charged with lime and gas under the pressure obtaining;

the liquid being thrown over growing vines or other plants in order to

destroy parasitic and other forms of life. The apparatus consists of a

metal cylinder fitted with straps so that it can be carried by man or

beast. At one end it has an attachment for a flexible pipe, at the other

end a perforated basket for carbide introduced and withdrawn through a

"man-hole" that can be tightly closed. The cylinder is filled with water

to a point just below the bottom of the basket when the basket is

uppermost; the carbide charge is then inserted, and the cover fastened

down. As long as the cylinder is carried in the same position, no

reaction between the carbide and the water occurs, and consequently no

pressure arises; but on inverting the vessel, the carbide is wetted, and

acetylene is liberated in the interior. On opening the cock on the outlet

pipe, a stream of liquid issues and may be directed as required. By

charging the cylinder in the first place with a solution of copper

sulphate, the liquid ejected becomes a solution and suspension of copper

and calcium salts and hydroxides, resembling "Bordeaux mixture," and may

be employed as such. In addition, it is saturated with acetylene which

adds to its value as a germicide.

The effective gas pressure set up in a closed generator has also been

employed in Italy to drive a gas-turbine, and so to produce motion. The

plant has been designed for use in lighthouses where acetylene is burnt,

and where a revolving or flashing light is required. The gas outlet from

a suitably arranged generator communicates with the inlet of a gas-

turbine, and the outlet of the turbine is connected to a pipe leading to

the acetylene burners. The motion of the turbine is employed to rotate

screens, coloured glasses, or any desired optical arrangements round the

flames; or, in other situations, periodically to open and close a cock on

the gas-main leading to the burners. In the latter case, a pilot flame

fed separately is always alight, and serves to ignite the gas issuing

from the main burners when the cock is opened.

Another use for acetylene, which is only dependent upon a suitably

lowered price for carbide to become of some importance, consists in the

preparation of a black pigment to replace ordinary lampblack. One method

for this purpose has been elaborated by Hubou. Acetylene is prepared from

carbide smalls or good carbide, according to price, and the gas is pumped

into small steel cylinders to a pressure of 2 atmospheres. An electric

spark is then passed, and the gas, standing at its limit of safety,

immediately dissociates, yielding a quantitative amount of hydrogen and

free carbon. The hydrogen is drawn off, collected in holders, and used

for any convenient purpose; the carbon is withdrawn from the vessel, and

is ready for sale. At present the pigment is much too expensive, at least

in British conditions, to be available in the manufacture of black paint;

but its price would justify its employment in the preparation of the best

grades of printers' ink. One of the authors has examined an average

sample and has found it fully equal in every way to blacks, such as those

termed "spirit blacks," which fetch a price considerably above their real

value. It has a pure black cast of tint, is free from greasy matter, and

can therefore easily be ground into water, or into linseed oil without

interfering with the drying properties of the latter. Acetylene black has

also been tried in calico printing, and has given far better results in

tone and strength than other blacks per unit weight of pigment. It may be

added that the actual yield of pigment from creosote oils, the commonest

raw material for the preparation of lampblack ("vegetable black"), seldom

exceeds 20 or 25 per cent., although the oil itself contains some 80 per

cent, of carbon. The yield from acetylene is clearly about 90 per cent.,

or from calcium carbide nearly 37.5 per cent, of the original weight.

An objection urged against the Hubou process is that only small

quantities of the gas can be treated with the spark at one time; if the

cylinders are too large, it is stated, tarry by-products are formed. A

second method of preparing lampblack (or graphite) from acetylene is that

devised by Frank, and depends on utilising the reactions between carbon

monoxide or dioxide and acetylene or calcium carbide, which have already

been sketched in Chapter VI. When acetylene is employed, the yield is

pure carbon, for the only by-product is water vapour; but if the carbide

process is adopted, the carbon remains mixed with calcium oxide. Possibly

such a material as Frank's carbide process would give, viz., 36 parts by

weight of carbon mixed with 56 parts of quicklime or 60 parts of carbon

mixed with 112 parts of quicklime, might answer the purpose of a pigment

in some black paints where the amount of ash left on ignition is not

subject to specification. Naturally, however, the lime might be washed

away from the carbon by treatment with hydrochloric acid; but the cost of

such a purifying operation would probably render the residual pigment too

expensive to be of much service except (conceivably) in the manufacture

of certain grades of printers' ink, for which purpose it might compete

with the carbon obtainable by the Hubou process already referred to.

Acetylene tetrachloride, or tetrachlorethane, C_2H_2Cl_4, is now produced

for sale as a solvent for chlorine, sulphur, phosphorus, and organic

substances such as fats. It may be obtained by the direct combination of

acetylene and chlorine as explained in Chapter VI., but the liability of

the reaction to take place with explosive violence would preclude the

direct application of it on a commercial scale. Processes free from such

risk have now, however, been devised for the production of

tetrachlorethane. One patented by the Salzbergwerk Neu-Stassfurt consists

in passing acetylene into a mixture of finely divided iron and chloride

of sulphur. The iron acts as a catalytic. The liquid is kept cool, and as

soon as the acetylene passes through unabsorbed, its introduction is

stopped and chlorine is passed in. Acetylene and chlorine are then passed

in alternately until the liquid finally is saturated with acetylene. The

tetrachlorethane, boiling at 147° C., is then distilled off, and the

residual sulphur is reconverted to the chloride for use again in the

process. A similar process in which the chlorine is used in excess is

applicable also to the production of hexachlorethane.

Dependent upon price, again, are several uses for calcium carbide as a

metallurgical or reducing reagent; but as those are uses for carbide only

as distinguished from acetylene, they do not fall within the purview of

the present book.

When discussing, in Chapter III., methods for disposing of the lime

sludge coming from an acetylene generator, it was stated that on occasion

a use could be found for this material. If the carbide has been entirely

decomposed in an apparatus free from overheating, the waste lime is

recovered as a solid mass or as a cream of lime practically pure white in

colour. Sometimes, however, as explained in Chapter II., the lime sludge

is of a bluish grey tint, even in cases where the carbide decomposed was

of good quality and there was no overheating in the generator. Such

discoloration is of little moment for most of the uses to which the

sludge may be put. The residue withdrawn from a carbide-to-water

generator is usually quite fluid; but when allowed to rest in a suitable

pit or tank, it settles down to a semi-solid or pasty mass which contains

on a rough average 47 per cent. of water and 53 per cent. of solid

matter, the amount of lime present, calculated as calcium oxide, being

about 40 per cent. Since 64 parts by weight of pure calcium carbide yield

74 parts of dry calcium hydroxide, it may be said that 1 part of ordinary

commercial carbide should yield approximately 1.1 parts of dry residue,

or 2.1 parts of a sludge containing 47 per cent. of moisture; and sludge

of this character has been stated by Vogel to weigh about 22.5 cwt. per

cubic yard.

Experience has shown that those pasty carbide residues can be employed

very satisfactorily, and to the best advantage from the maker's point of

view, by builders and decorators for the preparation of ordinary mortar

or lime-wash. The mortar made from acetylene lime has been found equal in

strength and other properties to mortar compounded from fresh slaked

lime; while the distemper prepared by diluting the sludge has been used

most successfully in all places where a lime-wash is required,

_e.g._, on fruit-trees, on cattle-pens, farm-buildings, factories,

and the "offices" of a residence. Many of the village installations

abroad sell their sludge to builders for the above-mentioned purposes at

such a price that their revenue accounts are materially benefited by the

additional income. The sludge is also found serviceable for softening the

feed-water of steam boilers by the common liming process; although it has

been stated that the material contains certain impurities--notably "fatty

matter"--which becomes hydrolysed by the steam, yielding fatty acids that

act corrosively upon the boiler-plates. This assertion would appear to

require substantiation, but a patent has been taken out for a process of

drying the sludge at a temperature of 150° to 200° C. in order to remove

the harmful matter by the action of the steam evolved. So purified, it is

claimed, the lime becomes fit for treating any hard potable or boiler-

feed water. It is very doubtful, however, whether the intrinsic value of

acetylene lime is such in comparison with the price of fresh lime that,

with whatever object in view, it would bear the cost of any method of

artificial drying if obtained from the generators in a pasty state.

When, on the other hand, the residue is naturally dry, or nearly so, it

is exactly equal to an equivalent quantity of quick or slaked lime as a

dressing for soil. In this last connexion, however, it must be remembered

that only certain soils are improved by an addition of lime in any shape,

and therefore carbide residues must not be used blindly; but if analysis

indicates that a particular plot of ground would derive benefit from an

application of lime, acetylene lime is precisely as good as any other

description. Naturally a residue containing unspent carbide, or

contaminated with tarry matter, is essentially valueless (except as

mentioned below); while it must not be forgotten that a solid residue if

it is exposed to air, or a pasty residue if not kept under water, will

lose many of its useful properties, because it will be partially

converted into calcium carbonate or chalk.

Nevertheless, in some respects, the residue from a good acetylene

generator is a more valuable material, agriculturally speaking, than pure

lime. It contains a certain amount of sulphur, &c., and it therefore

somewhat resembles the spent or gas lime of the coal-gas industry. This

sulphur, together, no doubt, with the traces of acetylene clinging to it,

renders the residue a valuable material for killing the worms and vermin

which tend to infest heavily manured and under-cultivated soil. Acetylene

lime has been found efficacious in exterminating the "finger-and-toe" of

carrots, the "peach-curl" of peach-trees, and in preventing cabbages from

being "clubbed." It may be applied to the ground alone, or after

admixture with some soil or stable manure. The residue may also be

employed, either alone or mixed with some agglomerate, in the

construction of garden paths and the like.

If the residues are suitably diluted with water and boiled with (say)

twice their original weight of flowers of sulphur, the product consists

of a mixture of various compounds of calcium and sulphur, or calcium

sulphides--which remain partly in solution and partly in the solid state.

This material, used either as a liquid spray or as a moist dressing, has

been said to prove a useful garden insecticide and weed-killer.

There are also numerous applications of the acetylene light, each of much

value, but involving no new principle which need be noticed. The light is

so actinic, or rich in rays acting upon silver salts, that it is

peculiarly useful to the photographer, either for portraiture or for his

various positive printing operations. Acetylene is very convenient for

optical lantern work on the small scale, or where the oxy-hydrogen or

oxy-coal-gas light cannot be used. Its intensity and small size make its

self-luminous flame preferable on optical grounds to the oil-lamp or the

coal-gas mantle; but the illuminating surface is nevertheless too large

to give the best results behind such condensers as have been carefully

worked to suit a source of light scarcely exceeding the dimensions of a

point. For lantern displays on very large screens, or for the projection

of a powerful beam of light to great distances in one direction (as in

night signalling, &c.), the acetylene blowpipe fed with pure oxygen, or

with air containing more than its normal proportion of oxygen, which is

discussed in Chapter IX., is specially valuable, more particularly if the

ordinary cylinder of lime is replaced by one of magnesia, zirconia, or

other highly refractory oxide.

CHAPTER XIII

PORTABLE ACETYLENE LAMPS AND PLANT

It will be apparent from what has been said in past chapters that the

construction of a satisfactory generator for portable purposes must be a

problem of considerable complexity. A fixed acetylene installation tends

to work the more smoothly, and the gas evolved therefrom to burn the more

pleasantly, the more technically perfect the various subsidiary items of

the plant are; that is to say, the more thoroughly the acetylene is

purified, dried, and delivered at a strictly constant pressure to the

burners and stoves. Moreover, the efficient behaviour of the generator

itself will depend more upon the mechanical excellence and solidity of

its construction than (with one or two exceptions) upon the precise

system to which it belongs. And, lastly, the installation will, broadly

speaking, work the better, the larger the holder is in proportion to the

demands ever made upon it; while that holder will perform the whole duty

of a gasholder more effectually if it belongs to the rising variety than

if it is a displacement holder. All these requirements of a good

acetylene apparatus have to be sacrificed to a greater or less extent in

portable generators; and since the sacrifice becomes more serious as the

generator is made smaller and lighter in weight, it may be said in

general terms that the smaller a portable (or, indeed, other) acetylene

apparatus is, the less complete or permanent satisfaction will it give

its user. Again, small portable apparatus are only needed to develop

intensities of light insignificant in comparison with those which may

easily be won from acetylene on a larger scale; they are therefore fitted

with smaller burners, and those burners are not merely small in terms of

consumption and illuminating power, but not infrequently are very badly

constructed, and are relatively deficient in economy or duty. Thus any

comparisons which may be made on lines similar to those adopted in

Chapter I., or between unit weights, volumes, or monetary equivalents of

calcium carbide, paraffin, candles, and colza oil, become utterly

incorrect if the carbide is only decomposed in a small portable generator

fitted with an inefficient jet; first, because the latent illuminating

power of the acetylene evolved is largely wasted; secondly, because any

gas produced over and above that capable of instant combustion must be

blown off from a vent-pipe; and thirdly, because the carbide itself tends

to be imperfectly decomposed, either through a defect in the construction

of the lamp, or through the brief and interrupted requirements of the

consumer.

In several important respects portable acetylene apparatus may be divided

into two classes from a practical point of view. There is the portable

table or stand lamp intended for use in an occupied room, and there is

the hand or supported lamp intended for the illumination of vehicles or

open-air spaces. Economy apart, no difficulty arises from imperfect

combustion or escape of unburnt gas from an outdoor lamp, but in a room

the presence of unburnt acetylene must always be offensive even if it is

not dangerous; while the combustion products of the impurities--and in a

portable generator acetylene cannot be chemically purified--are highly

objectionable. It is simply a matter of good design to render any form of

portable apparatus safe against explosion (employment of proper carbide

being assumed), for one or more vent-pipes can always be inserted in the

proper places; but from an indoor lamp those vent-pipes cannot be made to

discharge into a place of safety, while, as stated before, a generator in

which the vent-pipes come into action with any frequency is but an

extravagant piece of apparatus for the decomposition of so costly a

material as calcium carbide. Looked at from one aspect the holder of a

fixed apparatus is merely an economical substitute for the wasteful vent-

pipe, because it is a place in which acetylene can be held in reserve

whenever the make exceeds the consumption in speed. It is perhaps

possible to conceive of a large table acetylene lamp fitted with a water-

sealed rising holder; but for vehicular purposes the displacement holder

is practically the only one available, and in small apparatus it becomes

too minute in size to be of much service as a store for the gas produced

by after-generation. Other forms of holder have been suggested by

inventors, such as a collapsible bag of india-rubber or the like; but

rubber is too porous, weak, and perishable a material to be altogether

suitable. If it is possible, by bringing carbide and water into mutual

contact in predetermined quantities, to produce gas at a uniform rate,

and at one which corresponds with the requirements of the burner, in a

small apparatus--and experience has shown it to be possible within

moderately satisfactory limits--it is manifest that the holder is only

needed to take up the gas of after-generation; and in Chapters II. and

III. it was pointed out that after-generation only occurs when water is

brought into contact with an excess of carbide. If, then, the opposite

system of construction is adopted, and carbide is fed into water

mechanically, no after-generation can take place; and provided the make

of gas can be controlled in a small carbide-feed generator as accurately

as is possible in a small water-to-carbide generator, the carbide-feed

principle will exhibit even greater advantages in portable apparatus than

it does in plant of domestic size. Naturally almost every variety of

carbide-feeding gear, especially when small, requires or prefers

granulated (or granulated and "treated") carbide; and granulated carbide

must inevitably be considerably more expensive per unit of light evolved

than the large material, but probably in the application to which the

average portable acetylene apparatus is likely to be put, strict economy

is not of first consequence. In portable acetylene generators of the

carbide-feed type, the supply is generally governed by the movements of a

mushroom-headed or conical valve at the mouth of a conical carbide

vessel; such movements occurring in sympathy with the alterations in

level of the water in the decomposing chamber, which is essentially a

small displacement holder also, or being produced by the contraction of a

flexible chamber through which the gas passes on its way to the burner.

So far as it is safe to speak definitely on a matter of this kind, the

carbide-feed device appears to work satisfactorily in a stationary

(_e.g._, table) lamp; but it is highly questionable whether it could

be applied to a vehicular apparatus exposed to any sensible amount of

vibration. The device is satisfactory on the table of an occupied room so

far, be it understood, as any small portable generators can be: it has no

holder, but since no after-generation occurs, no holder is needed; still

the combustion products contaminate the room with all the sulphur and

phosphorus of the crude acetylene.

For vehicular lamps, and probably for hand lanterns, the water-to-carbide

system has practically no alternative (among actual generators), and

safety and convenience have to be gained at the expense of the carbide.

In such apparatus the supply of water is usually controlled ultimately by

pressure, though a hand-operated needle-valve is frequently put on the

water tube. The water actually reaches the carbide either by dropping

from a jet, by passing along, upwards or downwards, a "wick" such as is

used in oil-lamps, or by percolating through a mass of porous material

like felt. The carbide is held in a chamber closed except at the gas exit

to the burner and at the inlet from the water reservoir: so that if gas

is produced more rapidly than the burner takes it, more water is

prevented from entering, or the water already present is driven backwards

out of the decomposing chamber into some adjoining receptacle. It is

impossible to describe in detail all the lamps which have been

constructed or proposed for vehicular use; and therefore the subject must

be approached in general terms, discussing simply the principles involved

in the design of a safe portable generator.

In all portable apparatus, and indeed in generators of larger dimensions,

the decomposing chamber must be so constructed that it can never, even by

wrong manipulation, be sealed hermetically against the atmosphere. If

there is a cock on the water inlet tube which is capable of being

completely shut, there must be no cock between the decomposing chamber

and the burner. If there is a cock between the carbide vessel and the

burner, the water inlet tube must only be closed by the water, being

water-sealed, in fact, so that if pressure rises among the carbide the

surplus gas may blow the seal or bubble through the water in the

reservoir. If the water-supply is mainly controlled by a needle-valve, it

is useful to connect the burner with the carbide vessel through a short

length of rubber tube; and if this plan is adopted, a cock can, if

desired, be put close to the burner. The rubber should not be allowed to

form a bend hanging down, or water vapour, &c., may condense and

extinguish the flame. In any case there should be a steady fall from the

burner to the decomposing chamber, or to some separate catch-pit for the

products of condensation. Much of the success attainable with small

generators will depend on the water used. If it is contaminated with

undissolved matter, the dirt will eventually block the fine orifices,

especially the needle-valve, or will choke the pores of the wick or the

felt pad. If the water contains an appreciable amount of "temporary

hardness," and if it becomes heated much in the lamp, fur will be

deposited sooner or later, and will obviously give trouble. Where the

water reservoir is at the upper part of the lamp, and the liquid is

exposed to the heat of the flame, fur will appear quickly if the water is

hard. Considerable benefit would accrue to the user of a portable lamp by

the employment of rain water filtered, if necessary, through fabric or

paper. The danger of freezing in very severe weather may be prevented by

the use of calcium chloride, or preferably, perhaps, methylated spirit in

the water (_cf._ Chapter III., p. 92). The disfavour with which

cycle and motor acetylene lamps are frequently regarded by nocturnal

travellers, other than the users thereof, is due to thoughtless design in

the optical part of such lamps, and is no argument against the employment

of acetylene. By proper shading or deflection of the rays, the eyes of

human beings and horses can be sufficiently protected from the glare, and

the whole of the illumination concentrated more perfectly on the road

surface and the lower part of approaching objects--a beam of light never

reaching a height of 5 feet above the ground is all that is needed to

satisfy all parties.

As the size of the generator rises, conditions naturally become more

suited to the construction of a satisfactory apparatus; until generators

intended to supply light to the whole of (say) a railway carriage, or the

head and cab lamps of a locomotive, or for the outside and inside

lighting of an omnibus are essentially generators of domestic dimensions

somewhat altered in internal construction to withstand vibration and

agitation. As a rule there is plenty of space at the side of a locomotive

to carry a generator fitted with a displacement holder of sufficient

size, which is made tall rather than wide, to prevent the water moving

about more than necessary. From the boiler, too, steam can be supplied to

a coil to keep the liquid from freezing in severe weather. Such apparatus

need not be described at length, for they can be, and are, made on lines

resembling those of domestic generators, though more compactly, and

having always a governor to give a constant pressure. For carriage

lighting any ordinary type of generator, preferably, perhaps, fitted with

a displacement holder, can be erected either in each corridor carriage,

or in a brake van at the end of the train. Purifiers may be added, if

desired, to save the burners from corrosion; but the consumption of

unpurified gas will seldom be attended by hygienic disadvantages, because

the burners will be contained in closed lamps, ventilating into the

outside air. The generator, also, may conveniently be so constructed that

it is fed with carbide from above the roof, and emptied of lime sludge

from below the floor of the vehicle. It can hardly be said that the use

of acetylene generated on board adds a sensible risk in case of

collision. In the event of a subsequent fire, the gas in the generator

would burn, but not explode; but in view of the greater illuminating

power per unit volume of carbide than per equal volume of compressed oil-

gas, a portable acetylene generator should be somewhat less objectionable

than broken cylinders of oil-gas if a fire should follow a railway

accident of the usual kind. More particularly by the use of "cartridges"

of carbide, a railway carriage generator can be constructed of sufficient

capacity to afford light for a long journey, or even a double journey, so

that attention would be only required (in the ordinary way) at one end of

the line.

Passing on from the generators used for the lighting of vehicles and for

portable lamps for indoor lighting to the considerably larger portable

generators now constructed for the supply of acetylene for welding

purposes and for "flare" lamps, it will be evident that they may embody

most or all of the points which are essential to the proper working of a

fixed generator for the supply of a small establishment. The holder will

generally be of the displacement type, but some of these larger portable

generators are equipped with a rising holder. The generators are,

naturally, automatic in action, but may be either of the water-to-carbide

or carbide-to-water type--the latter being preferable in the larger sizes

intended for use with the oxy-acetylene blow-pipe for welding, &c., for

which use a relatively large though intermittent supply of acetylene is

called for. The apparatus is either carried by means of handles or poles

attached to it, or is mounted on a wheelbarrow or truck for convenience

of transport to the place where it is to be used. The so called "flare"

lamps, which are high power burners mounted, with or without a reflector,

above a portable generator, are extremely useful for lighting open spaces

where work has to be carried on temporarily after nightfall, and are

rapidly displacing oil-flares of the Lucigen type for such purposes.

The use of "cartridges" of calcium carbide has already been briefly

referred to in Chapters II. and III. These cartridges are usually either

receptacles of thin sheet-metal, say tin plate, or packages of carbide

wrapped up in grease proof paper or the like. If of metal, they may have

a lid which is detached or perforated before they are put into the

generator, or the generator (when automatic and of domestic size) may be

so arranged that a cartridge is punctured in one or more places whenever

more gas is required. If wrapped in paper, the cartridges may be dropped

into water by an automatic generator at the proper times, the liquid then

loosening the gum and so gaining access to the interior; or one spot may

be covered by a drape of porous material (felt) only, through which the

water penetrates slowly. The substance inside the cartridge may be

ordinary, granulated, or "treated" carbide. Cartridges or "sticks" of

carbide are also made without wrappings, either by moistening powdered

carbide with oil and compressing the whole into moulds, or by compressing

dry carbide dust and immersing the sticks in oil or molten grease. The

former process is said to cause the carbide to take up too much oil, so

that sticks made by the second method are reputed preferable. All these

cartridges have the advantage over common carbide of being more permanent

in damp air, of being symmetrical in shape, of decomposing at a known

speed, and of liberating acetylene in known quantity; but evidently they

are more expensive, owing to the cost of preparing them, &c. They may be

made more cheaply from the dust produced in the braking of carbide, but

in that case the yield of gas will be relatively low.

It is manifest that, where space is to spare, purifiers containing the

materials mentioned in Chapter V. can be added to any portable acetylene

apparatus, provided also that the extra weight is not prohibitive. Cycle

lamps and motor lamps must burn an unpurified gas unpurified from

phosphorus and sulphur; but it is always good and advisable to filter the

acetylene from dust by a plug of cotton wool or the like, in order to

keep the burners as clear as may be. A burner with a screwed needle for

cleaning is always advantageous. Formerly the burners used on portable

acetylene lamps were usually of the single jet or rat-tail, or the union

jet or fish tail type, and exhibited in an intensified form, on account

of their small orifices, all the faults of these types of burners for the

consumption of acetylene (see Chapter VIII.). Now, however, there are

numerous special burners adapted for use in acetylene cycle and motor

lamps, &c., and many of these are of the impinging jet type, and some

have steatite heads to prevent distortion by the heat. One such cycle-

lamp burner, as sold in England by L. Wiener, of Fore Street, London, is

shown in Fig. 21. A burner constructed like the "Kona" (Chapter VIII.) is

made in small sizes (6, 8 and 10 litres per hour) for use in vehicular

lamps, under the name of the "Konette," by Falk, Stadelmann and Co.,

Ltd., of London, who also make a number of other small impinging jet

burners. A single jet injector burner on the "Phôs" principle is made in

small sizes by the Phôs Co., of London, specially for use in lamps on

vehicles.

[Illustration: FIG. 21.--CYCLE-LAMP BURNER NO. 96042A.]

Nevertheless, although satisfactory medium-sized vehicular lamps for the

generation of acetylene have been constructed, the best way of using

acetylene for all such employments as these is to carry it ready made in

a state of compression. For railway purposes, where an oil-gas plant is

in existence, and where it is merely desired to obtain a somewhat

brighter light, the oil-gas may be enriched with 20 per cent. of

acetylene, and the mixed gas pumped into the same cylinders to a pressure

of 10 atmospheres, as mentioned in Chapter XI.; the only alteration

necessary being the substitution of suitable small burners for the common

oil-gas jets. As far as the plant is concerned, all that is required is a

good acetylene generator, purifier, and holder from which the acetylene

can be drawn or forced through a meter into a larger storage holder, the

meter being connected by gearing with another meter on the pipe leading

from the oil-gas holder to the common holder, so that the necessary

proportions of the two gases shall be introduced into the common holder

simultaneously. From this final holder the enriched gas will be pumped

into the cylinders or into a storage cylinder, by means of a thoroughly

cooled pump, so that the heat set free by the compression may be safely

dissipated.

Whenever still better light is required in railway carriages, as also for

the illumination of large, constantly used vehicles, such as omnibuses,

the acetone process (_cf._ Chapter XI.) exhibits notable advantages.

The light so obtained is the light of neat acetylene, but the gas is

acetylene having an upper limit of explosibility much lower than usual

because of the vapour of acetone in it. In all other respects the

presence of the acetone will be unnoticeable, for it is a fairly pure

organic chemical body, which burns in the flame completely to carbon

dioxide and water, exactly as acetylene itself does. If the acetylene is

merely compressed into porous matter without acetone, the gas burnt is

acetylene simply; but per unit of volume or weight the cylinders will not

be capable of developing so much light.

In the United States, at least one railway system (The Great Northern)

has a number of its passenger coaches lighted by means of plain acetylene

carried in a state of compression in cylinders without porous matter. The

gas is generated, filtered from dust, and stored in an ordinary rising

holder at a factory alongside the line; being drawn from this holder

through a drier to extract moisture, and through a safety device, by a

pump which, in three stages, compresses the acetylene into large storage

reservoirs. The safety device consists of a heavy steel cylinder filled

with some porous substance which, like the similar material of the

acetone cylinders, prevents any danger of the acetylene contained in the

water-sealed holder being implicated in an explosion starting backwards

from the compression, by extinguishing any spark which might be produced

there. The plant on the trains comprises a suitable number of cylinders,

filled by contact with the large stores of gas to a pressure of 10

atmospheres, pipes of fusible metal communicating with the lamps, and

ordinary half-foot acetylene burners. The cylinders are provided with

fusible plugs, so that, in the event of a fire, they and the service-

pipes would melt, allowing the gas to escape freely and burn in the air,

instead of exploding or dissociating explosively within the cylinders

should the latter be heated by any burning woodwork or the like. It is

stated that this plan of using acetylene enables a quantity of gas to be

carried under each coach which is sufficient for a run of from 53 to 70

hours' duration, or of over 3600 miles; that is to say, enables the

train, in the conditions obtaining on the line in question, to make a

complete "round trip" without exhaustion of its store of artificial

light. The system has been in operation for some years, and appears to

have been so carefully managed that no accident has arisen; but it is

clear that elements of danger are present which are eliminated when the

cylinders are loaded with porous matter and acetone. The use of a similar

system of compressed acetylene train lighting in South America has been

attended with a disastrous explosion, involving loss of life.

It may safely be said that the acetone system, or less conveniently

perhaps the mere compression into porous matter, is the best to adopt for

the table-lamp which is to be used in occupied rooms Small cylinders of

such shapes as to form an elegant base for a table-lamp on more or less

conventional lines would be easy to make. They would be perfectly safe to

handle. If accidentally or wilfully upset, no harm would arise. By

deliberate ill-treatment they might be burst, or the gas-pipe fractured

below the reducing valve, so that gas would escape under pressure for a

time; but short of this they would be as devoid of extra clangor in times

of fire as the candle or the coal-gas burner. Moreover, they would only

contaminate the air with carbon dioxide and water vapour, for the gas is

purified before compression; and modern investigations have conclusively

demonstrated that the ill effects produced in the air of an imperfectly

ventilated room by the extravagant consumption of coal-gas depend on the

accumulation of the combustion products of the sulphur in the gas rather

than upon the carbon dioxide set free.

One particular application of the portable acetylene apparatus is of

special interest. As calcium carbide evolves an inflammable gas when it

merely comes into contact with water, it becomes possible to throw into

the sea or river, by hand or by ejection from a mortar, a species of bomb

or portable generator which is capable of emitting a powerful beam of

light if only facilities are present for inflaming the acetylene

generated; and it is quite easy so to arrange the interior of such

apparatus that they can be kept ready for instant use for long periods of

time without sensible deterioration, and that they can be recharged after

employment. Three methods of firing the gas have been proposed. In one

the shock or contact with the water brings a small electric battery into

play which produces a spark between two terminals projecting across the

burner orifice; in the second, a cap at the head of the generator

contains a small quantity of metallic potassium, which decomposes water

with such energy that the hydrogen liberated catches fire; and in the

third a similar cap is filled with the necessary quantity of calcium

phosphide, or the "carbophosphide of calcium" mentioned in Chapter XI.,

which yields a flame by the immediate ignition of the liquid phosphine

produced on the attack of water. During the two or three seconds consumed

in the production of the spark or pilot flame, the water is penetrating

the main charge of calcium carbide in the interior of the apparatus,

until the whole is ready to give a bright light for a time limited only

by the capacity of the generator. It is obvious that such apparatus may

be of much service at sea: they may be thrown overboard to illuminate

separate lifebuoys in case of accident, or be attached to the lifebuoys

they are required to illuminate, or be used as lifebuoys themselves if

fitted with suitable chains or ropes; they may be shot ahead to

illuminate a difficult channel, or to render an enemy visible in time of

war. Several such apparatus have already been constructed and severely

tested; they appear to give every satisfaction. They are, of course, so

weighted that the burner floats vertically, while buoyancy is obtained

partly by the gas evolved, and partly by a hollow portion of the

structure containing air. Cartridges of carbide and caps yielding a self-

inflammable gas can be carried on board ship, by means of which the

torches or lifebuoys may be renewed after service in a few minutes' time.

CHAPTER XIV

VALUATION AND ANALYSIS OF CARBIDE

The sale and purchase of calcium carbide in this country will, under

existing conditions, usually be conducted in conformity with the set of

regulations issued by the British Acetylene Association, of which a copy,

revised to date, is given below:

"REGULATIONS AS TO CARBIDE OF CALCIUM."

1. The carbide shall be guaranteed by the seller to yield, when broken

to standard size, _i.e._, in lumps varying from 1 to 2-1/2 inches or

larger, not less than 4.8 cubic feet per lb., at a barometric pressure of

30 inches and temperature of 60° Fahr. (15.55° Centigrade). The actual

gas yield shall be deemed to be the gas yield ascertained by the analyst,

plus 5 per cent.

"Carbide yielding less than 4.8 cubic feet in the sizes given above shall

be paid for in proportion to the gas yield, _i.e._, the price to be

paid shall bear the same relation to the contract price as the gas yield

bears to 4.8 cubic feet per lb.

"2. The customer shall have the right to refuse to take carbide yielding

in the sizes mentioned above less than 4.2 cubic foot, per lb., and it

shall lie, in case of refusal and as from the date of the result, of the

analysis being made known to either party, at the risk and expense of the

seller.

"3. The carbide shall not contain higher figures of impurities than shall

from time to time be fixed by the Association.

"4. No guarantee shall be given for lots of less than 3 cwt., or for

carbide crushed to smaller than the above sizes.

"5. In case of dispute as to quality, either the buyer or the seller

shall have the right to have one unopened drum per ton of carbide, or

part of a ton, sent for examination to one of the analysts appointed by

the Association, and the result of the examination shall be held to apply

to the whole of the consignment to which the drum belonged.

"6. A latitude of 5 per cent, shall be allowed for analysis; consequently

differences of 5 per cent. above or below the yields mentioned in 1 and 2

shall not be taken into consideration.

"7. Should the yield of gas be less than 4.8 cubic feet less 5 per cent.,

the carriage of the carbide to and from the place of analysis and the

cost of the analysis shall be paid for by the seller. Should the yield be

more than 4.8 cubic feet less 5 per cent., the carriage and costs of

analysis shall be borne by the buyer, who, in addition, shall pay an

increase of price for the carbide proportionate to the gas yield above

4.8 cubic feet plus 5 per cent.

"8. Carbide of 1 inch mesh and above shall not contain more than 5 per

cent. of dust, such dust to be defined as carbide capable of passing

through a mesh of one-sixteenth of an inch.

"9. The seller shall not be responsible for deterioration of quality

caused by railway carriage in the United Kingdom, unless he has sold

including carriage to the destination indicated by the buyer.

"10. Carbide destined for export shall, in case the buyer desires to have

it tested, be sampled at the port of shipment, and the guarantee shall

cease after shipment.

"11. The analyst shall take a sample of not less than 1 lb. each from the

top, centre, and bottom of the drum. The carbide shall be carefully

broken up into small pieces, due care being taken to avoid exposure to

the air as much as possible, carefully screened and tested for gas yield

by decomposing it in water, previously thoroughly saturated by exposure

to acetylene for a period of not less than 48 hours.

"12. Carbide which, when properly decomposed, yields acetylene containing

from all phosphorus compounds therein more than .05 per cent. by volume

of phosphoretted hydrogen, may be refused by the buyer, and any carbide

found to contain more than this figure, with a latitude of .01 per cent.

for the analysis, shall lie at the risk and expense of the seller in the

manner described in paragraph 2.

"The rules mentioned in paragraph 7 shall apply as regards the carriage

and costs of analysis; in other words, the buyer shall pay these costs if

the figure is below 0.05 per cent. plus 0.01 per cent., and the seller if

the figure is above 0.05 per cent. plus 0.01 per cent.

"The sampling shall take place in the manner prescribed in paragraphs 5

and 11, and the analytical examination shall be effected in the manner

prescribed by the Association and obtainable upon application to the

Secretary."

* * * * *

The following is a translation of the corresponding rules issued by the

German Acetylene Association (_Der Deutsche Acetylenverein_) in

regard to business dealings in calcium carbide, as put into force on

April 1, 1909:

"REGULATIONS OF THE GERMAN ACETYLENE ASSOCIATION FOR TRADE IN CARBIDE.

"_Price_.

"The price is to be fixed per 100 kilogrammes (= 220 lb.) net weight of

carbide in packages containing about 100 kilogrammes.

"By packages containing about 100 kilogrammes are meant packages

containing within 10 per cent. above or below that weight.

"The carbide shall be packed in gas- and water-tight vessels of sheet-

iron of the strength indicated in the prescriptions of the carrying

companies.

"The prices for other descriptions of packing must be specially stated.

"_Place of Delivery_.

"For consignment for export, the last European shipping port shall be

taken as the place of delivery.

"_Quality_.

"Commercial carbide shall be of such quality that in the usual lumps of

15 to 80 mm. (about 3/5 to 3 inches) diameter it shall afford a yield of

at least 300 litres at 15° C. and 760 mm. pressure of crude acetylene per

kilogramme for each consignment (= 4.81 cubic feet at 60° F. and 30

inches per lb.). A margin of 2 per cent. shall be allowed for the

analysis. Carbide which yields less than 300 litres per kilogramme, but

not less than 270 litres (= 4.33 cubic feet) of crude acetylene per

kilogramme (with the above-stated 2 per cent. margin for analysis) must

be accepted by the buyer. The latter, however, is entitled to make a

proportionate deduction from the price and also to deduct the increased

freight charges to the destination or, if the latter is not settled at

the time when the transaction is completed, to the place of delivery.

Carbide which yields less than 270 litres of crude acetylene per

kilogramme need not be accepted.

"Carbide must not contain more than 5 per cent. of dust. By dust is to be

understood all which passes through a screen of 1 mm. (0.04 inch) square,

clear size of holes.

"Small carbide of from 4 to 15 mm. (= 1/6 to 3/5 inch) in size (and

intermediate sizes) must yield on the average for each delivery at least

270 litres at 15° C. and 760 mm. pressure of crude acetylene per

kilogramme (= 4.33 cubic feet at 60° F. and 30 inches per lb.) A margin

of 2 per cent. shall be allowed for the analysis. Small carbide of from 4

to 15 mm. in size (and intermediate sizes) which yields less than 270

litres but not less than 250 litres (= 4.01 cubic feet per lb.) of crude

acetylene per kilogramme (with the above-stated 2 per cent. margin for

analysis) must be accepted by the buyer. The latter, however, is entitled

to make a proportionate deduction from the price and also to deduct the

increased freight charges to the destination or, if the latter is not

settled at the time when the transaction is completed, to the place of

delivery. Small carbide of from 4 to 15 mm. in size (and intermediate

sizes) which yields less than 250 litres per kilogramme need not be

accepted.

"Carbide shall only be considered fit for delivery if the proportion of

phosphoretted hydrogen in the crude acetylene does not amount to more

than 0.04 volume per cent. A margin of 0.01 volume per cent. shall be

allowed for the analysis for phosphoretted hydrogen. The whole of the

phosphorus compounds contained in the gas are to be calculated as

phosphoretted hydrogen.

"_Period for Complaints._

"An interval of four weeks from delivery shall be allowed for complaints

for consignments of 5000 kilogrammes (= 5 tons) and over, and an interval

of two weeks for smaller consignments. A complaint shall refer only to a

quantity of carbide remaining at the time of taking the sample.

"_Determination of Quality._

"1. In case the parties do not agree that the consignee is to send to the

analyst for the determination of the quality one unopened and undamaged

drum when the consignment is less than 5000 kilogrammes, and two such

drums when it is over 5000 kilogrammes, a sample for the purpose of

testing the quality is to be taken in the following manner:

"A sample having a total weight of at least 2 kilogrammes (= 4.4 lb.) is

to be taken. If the delivery to be tested does not comprise more than ten

drums, the sample is to be taken from an unopened and undamaged drum

selected at random. With deliveries of more than ten drums, the sample is

to be drawn from not fewer than 10 per cent, of the lot, and from each of

the unopened and undamaged drums drawn for the purpose not less than 1

kilogramme (= 2.2 lb.) is to be taken.

"The sampling is to be carried out by a trustworthy person appointed by

the two parties, or by one of the experts regularly recognised by the

German Acetylene Association, thus: Each selected drum, before opening,

is to be turned over twice (to got rid of any local accumulation of dust)

and the requisite quantity is to be withdrawn with a shovel (not with the

hand) from any part of it. These samples are immediately shot into one or

more vessels which are closed air- and water-tight. The lid is secured by

a seal. No other description of package, such as cardboard cases, boxes,

&c., is permissible.

"If there is disagreement as to the choice of a trustworthy person, each

of the two parties is to take the required quantity, as specified above.

Acetylene, the Principles of Its Generation and Use A Practical Handbook on the Production, Purification, and Subsequent Treatment of Acetylene for the Development of Light, Heat, and Power · 第 20 / 22 章

AUTOGENOUS SOLDERING AND WELDING.--The blowpipe is suitable for the