USE OF OIL IN GENERATORS.--Calcium carbi_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

capable of attack for the purpose of evolving acetylene by a liquid that

is essentially water, or by one that contains some water mixed with it.

Oils and the like, or even such non-aqueous liquids as absolute alcohol,

have no effect upon carbide, except that the former naturally make it

greasy and somewhat more difficult to moisten. This last property has

been found of service in acetylene generation, especially on the small

scale; for if carbide is soaked in, or given a coating of, some oil, fat,

or solid hydrocarbon like petroleum, cocoanut oil, or paraffin wax, the

substance becomes comparatively indifferent towards water vapour or the

moisture present in the air, while it still remains capable of complete,

albeit slow, decomposition by liquid water when completely immersed

therein. The fact that ordinary calcium carbide is attacked so quickly by

water is really a defect of the substance; for it is to this extreme

rapidity of reaction that the troubles of overheating are due. Now, if

the basket in the generator B^1 of Fig. 2, or, indeed, the carbide store

in any of the carbide-to-water apparatus, is filled with a carbide which

has been treated with oil or wax, as long as the water-level stands at

_l'_ and _l"_ or the carbide still remains in the hopper, it is

essentially unattacked by the vapour arising from the liquid; but

directly the basket is submerged, or the lumps fall into the water,

acetylene is produced, and produced more slowly and regularly than

otherwise. Again, oils do not mix with water, but usually float thereon,

and a mass of water covered by a thick film or layer of oil does not

evaporate appreciably. If, now, a certain quantity of oil, say lamp

paraffin or mineral lubricating oil, is poured on to the water in B^1,

Fig. 2, it moves upwards and downwards with the water. When the water

takes the position _l_, the oil is driven upwards away from the

basket of carbide, and acetylene is generated in the ordinary manner; but

when the water falls to _l"_ the oil descends also, rinses off much

of the adhering water from the carbide lumps, covers them with a greasy

film, and almost entirely stops generation till it is in turn washed off

by the next ascent of the water. Similarly, if the carbide in generators

F, G, and H (also K) has been treated with a solid or semi-solid grease,

it is practically unattacked by the stream of warm damp gas, and is only

decomposed when the liquid itself arrives in the basket. For the same

reason treated carbide can be kept for fairly long periods of time, even

in a drum with badly fitting lid, without suffering much deterioration by

the action of atmospheric moisture. The problem of acetylene generation

is accordingly simplified to a considerable degree by the use of such

treated carbide, and the advantage becomes more marked as the plant

decreases in size till a portable apparatus is reached, because the

smaller the installation the more relatively expensive or inconvenient is

a large holder for surplus gas. The one defect of the method is the extra

cost of such treated carbide; and in English conditions ordinary calcium

carbide is too expensive to permit of any additional outlay upon the

acetylene if it is to compete with petroleum or the product of a tiny

coal-gas works. The extra cost of using treated carbide falls upon the

revenue account, and is much more noticeable than that of a large holder,

which is capital expenditure. When fluid oil is employed in a generator

of type B^1, evolution of gas becomes so regular that any holder beyond

the displacement one which the apparatus itself constitutes is actually

unnecessary, though still desirable; but B^1, with or without oil, still

remains a displacement apparatus, and as such gives no constant pressure.

It must be admitted that the presence of oil so far governs the evolution

of gas that the movement of the water, and the consequent variation of

pressure, is rendered very small; still a governor or a rising holder

would be required to give the best result at the burners. One point in

connexion with the use of liquid oil must not be overlooked, viz., the

extra trouble it may give in the disposal of the residues. This matter

will be dealt with more fully in Chapter V.; here it is sufficient to say

that as the oil does not mix with the water but floats on the surface,

care has to be taken that it is not permitted to enter any open stream.

The foregoing remarks about the use of oil manifestly only apply to those

cases where it is used in quantity and where it ultimately becomes mixed

with the sludge or floats on the water in the decomposing chamber. The

employment of a limpid oil, such as paraffin, as an intermediate liquid

into which carbide is introduced on its way to the water in the

decomposing vessel of a hand-fed generator in the manner described on

page 70 is something quite different, because, except for trifling

losses, one charge of oil should last indefinitely.

RISING GASHOLDERS.--Whichever description of holder is employed in an

acetylene apparatus, the gas is always stored over, or in contact with, a

liquid that is essentially water. This introduces three subjects for

consideration: the heavy weight of a large body of liquid, the loss of

gas by dissolution in that liquid, and the protection of that liquid from

frost in the winter. The tanks of rising holders are constructed in two

different ways. In one the tank is a plain cylindrical vessel somewhat

larger in diameter than the bell which floats in it; and since there must

be nearly enough water in the tank to fill the interior of the bell when

the latter assumes its lowest position, the quantity of water is

considerable, its capacity for dissolving acetylene is large, and the

amount of any substance that may have to be added to it to lower its

freezing-point becomes so great as to be scarcely economical. All these

defects, including that of the necessity for very substantial foundations

under the holder to support its enormous weight, may be overcome by

adopting the second method of construction. It is clear that the water in

the centre of the tank is of no use,--all that is needed being a narrow

trough for the bell to work in. Large rising holders are therefore

advantageously built with a tank formed in the shape of an annulus, the

effective breadth of which is not more than 2 or 3 inches, the centre

portion being roofed over so as to prevent escape of gas. The same

principle may be retained with modified details by fitting inside a plain

cylindrical tank a "dummy" or smaller cylinder, closed by a flat or

curved top and fastened water- and air-tight to the bottom of the main

vessel. The construction of annular tanks or the insertion of a "dummy"

may be attended with difficulty if the tank is wholly or partly sunk

below the ground level, owing to the lifting force of water in the

surrounding soil. Where a steel tank is sunk, or a masonry tank is

constructed, regard must be paid, both in the design of the tank and in

the manner of construction, to the level of the underground water in the

neighbourhood, as in certain cases special precautions will be needed to

avoid trouble from the pressure of the water on the outside of the tank

until it is balanced by the pressure of the water with which the tank is

filled. So far as mere dissolution of gas is concerned, the loss may be

reduced by having a circular disc of wood, &c., a little smaller in

diameter than the boll, floating on the water of a plain tank.

EFFECT OF STORAGE IN GASHOLDER ON ACETYLENE.--It is perfectly true, as

has been stated elsewhere, that the gas coming from an acetylene

generator loses some of its illuminating power if it is stored over water

for any great length of time; such loss being given by Nichols as 94 per

cent, in five months, and having been found by one of the authors as 0.63

per cent. per day--figures which stand in fair agreement with one

another. This wastage is not due to any decomposition of the acetylene in

contact with water, but depends on the various solubilities of the

different gases which compose the product obtained from commercial

calcium carbide. Inasmuch as an acetylene evolved in the best generator

contains some foreign ingredients, and inasmuch as an inferior product

contains more (_cf._ Chapter V.), the contents of a holder are never

pure; but as those contents are principally made up of acetylene itself,

that gas stands at a higher partial pressure in the holder than the

impurities. Since acetylene is more soluble in water than any of its

diluents or impurities, sulphuretted hydrogen and ammonia excepted, and

since the solubility of all gases increases as the pressure at which they

are stored rises, the true acetylene in an acetylene holder dissolves in

the water more rapidly and comparatively more copiously than the

impurities; and thus the acetylene tends to disappear and the impurities

to become concentrated within the bell. Simultaneously at the outer part

of the seal, air is dissolved in the water; and by processes of diffusion

the air so dissolved passes through the liquid from the outside to the

inside, where it escapes into the bell, while the dissolved acetylene

similarly passes from the inside to the outside of the seal, and there

mingles with the atmosphere. Thus, the longer a certain volume of

acetylene is stored over water, the more does it become contaminated with

the constituents of the atmosphere and with the impurities originally

present in it; while as the acetylene is much more soluble than its

impurities, more gas escapes from, than enters, the holder by diffusion,

and so the bulk of stored gas gradually diminishes. However, the figures

previously given show that this action is too slow to be noticeable in

practice, for the gas is never stored for more than a few days at a time.

The action cannot be accepted as a valid argument against the employment

of a holder in acetylene plant. Such deterioration and wastage of gas may

be reduced to some extent by the use of a film of some cheap and

indifferent oil floating on the water inside an acetylene holder; the

economy being caused by the lower solubility of acetylene in oils than in

aqueous liquids not saturated with some saline material. Probably almost

any oil would answer equally well, provided it was not volatile at the

temperature of the holder, and that it did not dry or gum on standing,

_e.g._, olive oil or its substitutes; but mineral lubricating oil is

not so satisfactory. It is, however, not necessary to adopt this method

in practice, because the solvent power of the liquid in the seal can be

reduced by adding to it a saline body which simultaneously lowers its

freezing-point and makes the apparatus more trustworthy in winter.

FREEZING OF GASHOLDER SEAL.--The danger attendant upon the congelation of

the seal in an acetylene holder is very real, not so much because of the

fear that the apparatus may be burst, which is hardly to be expected, as

because the bell will be firmly fixed in a certain position by the ice,

and the whole establishment lighted by the gas will be left in darkness.

In these circumstances, hurried and perhaps injudicious attempts may be

made to thaw the seal by putting red-hot bars into it or by lighting

fires under it, or the generator-house may be thoughtlessly entered with

a naked light at a time when the apparatus is possibly in disorder

through the loss of storage-room for the gas it is evolving. Should a

seal ever freeze, it must be thawed only by the application of boiling

water; and the plant-house must be entered, if daylight has passed, in

perfect darkness or with the assistance of an outside lamp whining

through a closed window. [Footnote: By "closed window" is to be

understood one incapable of being opened, fitted with one or two

thicknesses of stout glass well puttied in, and placed in a wall of the

house as far as possible from the door.] There are two ways of preventing

the seal from freezing. In all large installations the generator-house

will be fitted with a warm-water heating apparatus to protect the portion

of the plant where the carbide is decomposed, and if the holder is also

inside the same building it will naturally be safe. If it is outside, one

of the flow-pipes from the warming apparatus should be led into and round

the lowest part of the seal, care being taken to watch for, or to provide

automatic arrangements for making good, loss of water by evaporation. If

the holder is at a distance from the generator-house, or if for any other

reason it cannot easily be brought into the warming circuit, the seal can

be protected in another way; for unlike the water in the generator, the

water in the holder-seal will perform its functions equally well however

much it be reduced in temperature, always providing it is maintained in

the liquid condition. There are numerous substances which dissolve in, or

mix with, water, and yield solutions or liquids that do not solidify

until their temperature falls far below that of the natural freezing-

point. Assuming that those substances in solution do not attack the

acetylene, nor the metal of which the holder is built, and are not too

expensive, choice may be made between them at will. Strictly speaking the

cost of using them is small, because unless the tank is leaky they last

indefinitely, not evaporating with the water as it is vaporised into the

gas or into the air. The water-seal of a holder standing within the

generator-house may eventually become so offensive to the nostrils that

the liquid has to be renewed; but when this happens it is due to the

accumulation in the water of the water-soluble impurities of the crude

acetylene. If, as should be done, the gas is passed through a washer or

condenser containing much water before it enters the holder the

sulphuretted hydrogen and ammonia will be extracted, and the seal will

not acquire an obnoxious odour for a very long time.

Four principal substances have been proposed for lowering the freezing-

point of the water in an acetylene-holder seal; common salt (sodium

chloride), calcium chloride (not chloride of lime), alcohol (methylated

spirit), and glycerin. A 10 per cent. solution of common salt has a

specific gravity of 1.0734, and does not solidify above -6° C. or 21.2°

F.; a 15 per cent. solution has a density of 1.111, and freezes at -10°

C. or 14° F. Common salt, however, is not to be recommended, as its

solutions always corrode iron and steel vessels more or less quickly.

Alcohol, in its English denatured form of methylated spirit, is still

somewhat expensive to use, but it has the advantage of not increasing the

viscosity of the water; so that a frost-proof mixture of alcohol and

water will flow as readily through minute tubes choked with needle-

valves, or through felt and the like, or along wicks, as will plain

water. For this reason, and for the practically identical one that it is

quite free from dirt or insoluble matter, diluted spirit is specially

suitable for the protection of the water in cyclists' acetylene lamps,

[Footnote: As will appear in Chapter XIII., there is usually no holder in

a vehicular acetylene lamp, all the water being employed eventually for

the purpose of decomposing the carbide. This does not affect the present

question. Dilute alcohol does not attack calcium carbide so energetically

as pure water, because it stands midway between pure water and pure

alcohol, which is inert. The attack, however, of the carbide is as

complete as that of pure water, and the slower speed thereof is a

manifest advantage in any holderless apparatus.] where strict economy is

less important than smooth working. For domestic and larger installations

it is not indicated. As between calcium chloride and glycerin there is

little to choose; the former will be somewhat cheaper, but the latter

will not be prohibitively expensive if the high-grade pure glycerins of

the pharmacist are avoided. The following tables show the amount of each

substance which must be dissolved in water to obtain a liquid of definite

solidifying point. The data relating to alcohol were obtained by Pictet,

and those for calcium chloride by Pickering. The latter are materially

different from figures given by other investigators, and perhaps it would

be safer to make due allowance for this difference. In Germany the

Acetylene Association advocates a 17 per cent. solution of calcium

chloride, to which Frank ascribes a specific gravity of 1.134, and a

freezing-point of -8° C. or 17.6° F.

_Freezing-Points of Dilute Alcohol._

_________________________________________________________

| | | |

| Percentage of | Specific Gravity. | Freezing-point. |

| Alcohol. | | |

|_______________|___________________|_____________________|

| | | | |

| 4.8 | 0.9916 | -2.0 | +28.4 |

| 11.3 | 0.9824 | 5.0 | 23.0 |

| 16.4 | 0.9761 | 7.5 | 18.5 |

| 18.8 | 0.9732 | 9.4 | 15.1 |

| 20.3 | 0.9712 | 10.6 | 12.9 |

| 22.1 | 0.9689 | 12.2 | 10.0 |

| 24.2 | 0.9662 | 14.0 | 6.8 |

| 26.7 | 0.9627 | 16.0 | 3.2 |

| 29.9 | 0.9578 | 18.9 | -2.0 |

|_______________|___________________|__________|__________|

_Freezing-Points of Dilute Glycerin._

_________________________________________________________

| | | |

| Percentage of | Specific Gravity. | Freezing-point. |

| Glycerin. | | |

|_______________|___________________|_____________________|

| | | | |

| 10 | 1.024 | -1.0 | +30.2 |

| 20 | 1.051 | 2.5 | 27.5 |

| 30 | 1.075 | 6.0 | 21.2 |

| 40 | 1.105 | 17.5 | 0.5 |

| 50 | 1.127 | 31.3 | -24.3 |

|_______________|___________________|__________|__________|

_Freezing-Points of Calcium Chloride Solutions._

_________________________________________________________

| | | |

| Percentage of | Specific Gravity. | Freezing-point. |

| CaCl_2. | | |

|_______________|___________________|_____________________|

| | | | |

| 6 | 1.05 | -3.0 | +26.6 |

| 8 | 1.067 | 4.3 | 24.3 |

| 10 | 1.985 | 5.9 | 21.4 |

| 12 | 1.103 | 7.7 | 18.1 |

| 14 | 1.121 | 9.8 | 14.4 |

| 16 | 1.140 | 12.2 | 10.0 |

| 18 | 1.159 | 15.2 | 4.6 |

| 20 | 1.170 | 18.6 | -1.5 |

|_______________|___________________|__________|__________|

Calcium chloride will probably be procured in the solid state, but it can

be purchased as a concentrated solution, being sold under the name of

"calcidum" [Footnote: This proprietary German article is a liquid which

begins to solidify at -42° C. (-43.6° F.), and is completely solid at

-56° C. (-69)° F.). Diluted with one-third its volume of water, it

freezes between -20° and -28° C. (-4° and-l8.4° F.). The makers recommend

that it should be mixed with an equal volume of water. Another material

known as "Gefrierschutzflüssigkeit" and made by the Flörsheim chemical

works, freezes at -35° C. (-3° F.). Diluted with one-quarter its volume

of water, it solidifies at -18° C. (-0.4° F.); with equal parts of water

it freezes at -12° C. (10.4° F.). A third product, called "calcidum

oxychlorid," has been found by Caro and Saulmann to be an impure 35 per

cent. solution of calcium chloride. Not one of these is suitable for

addition to the water used in the generating chamber of an acetylene

apparatus, the reasons for this having already been mentioned.] for the

protection of gasholder seals. Glycerin itself resembles a strong

solution of calcium chloride in being a viscid, oily-looking liquid; and

both are so much heavier than water that they will not mix with further

quantities unless they are thoroughly agitated therewith. Either may be

poured through water, or have water floated upon it, without any

appreciable admixture taking place; and therefore in first adding them to

the seal great care must be taken that they are uniformly distributed

throughout the liquid. If the whole contents of the seal cannot

conveniently be run into an open vessel in which the mixing can be

performed, the sealing water must be drawn off a little at a time and a

corresponding quantity of the protective reagent added to it. Care must

be taken also that motives of economy do not lead to excessive dilution

of the reagent; the seal must be competent to remain liquid under the

prolonged influence of the most severe frost ever known to occur in the

neighbourhood where the plant is situated. If the holder is placed out of

doors in an exposed spot where heavy rains may fall on the top of the

bell, or where snow may collect there and melt, the water is apt to run

down into the seal, diluting the upper layers until they lose the frost-

resisting power they originally had. This danger may be prevented by

erecting a sloping roof over the bell crown, or by stirring up the seal

and adding more preservative whenever it has been diluted with rain

water. Quite small holders would probably always be placed inside the

generator-house, where their seals may be protected by the same means as

are applied to the generator itself. It need hardly be said that all

remarks about the dangers incidental to the freezing of holder seals and

the methods for obviating them refer equally to every item in the

acetylene plant which contains water or is fitted with a water-sealed

cover; only the water which is actually used for decomposing the calcium

carbide cannot be protected from frost by the addition of calcium

chloride or glycerin--that water must be kept from falling to its natural

freezing-point. From Mauricheau-Beaupré's experiments, referred to on

page 106, it would appear that a further reason for avoiding an addition

of calcium chloride to the water used for decomposing carbide should lie

in the danger of causing a troublesome production of froth within the

generator.

It will be convenient to digress here for the purpose of considering how

the generators of an acetylene apparatus themselves should be protected

from frost; but it may be said at the outset that it is impossible to lay

down any fixed rules applicable to all cases, since local conditions,

such as climate, available resources, dimensions, and exposed or

protected position of the plant-house vary so largely in different

situations. In all important installations every item of the plant,

except the holder, will be collected in one or two rooms of a single

building constructed of brick or other incombustible material. Assuming

that long-continued frost reigns at times in the neighbourhood, the whole

of such a building, with the exception of one apartment used as a carbide

store only, is judiciously fitted with a heating arrangement like those

employed in conservatories or hothouses; a system of pipes in which warm

water is kept circulating being run round the walls of each chamber near

the floor. The boiler, heated with coke, paraffin, or even acetylene,

must naturally be placed in a separate room of the apparatus-house having

no direct (indoor) communication with the rooms containing the

generators, purifiers, &c. Instead of coils of pipe, "radiators" of the

usual commercial patterns may be adopted; but the immediate source of

heat should be steam, or preferably hot water, and not hot air or

combustion products from the stove. In exposed situations, where the

holder is out of doors, one branch of the flow-pipe should enter and

travel round the seal as previously suggested. Most large country

residences are already provided with suitable heating apparatus for

warming the greenhouses, and part of the heat may be capable of diversion

into the acetylene generator-shed if the latter is erected in a

convenient spot. In fact, if any existing hot-water warming appliances

are already at hand, and if they are powerful enough to do a little more

work, it may be well to put the generator-building in such a position

that it can be efficiently supplied with artificial warmth from those

boilers; for any extra length of main necessary to lead the gas into the

residence from a distant generator will cost less on the revenue account

than the fuel required to feed a special heating arrangement. In smaller

installations, especially such as are to be found in mild climates, it

may be possible to render the apparatus-house sufficiently frost-proof

without artificial heat by building it partly underground, fitting it

with a double skylight in place of a window for the entrance of daylight,

and banking up its walls all round with thick layers of earth. The house

must have a door, however, which must open outwards and easily, so that

no obstacle may prevent a hurried exit in emergencies. Such a door can

hardly be made very thick or double without rendering it heavy and

difficult to open; and the single door will be scarcely capable of

protecting the interior if the frost is severe and prolonged.

Ventilators, too, must be provided to allow of the escape of any gas that

may accidentally issue from the plant during recharging, &c.; and some

aperture in the roof will be required for the passage of the vent pipe or

pipes, which, in certain types of apparatus, move upwards and downwards

with the bell of the holder. These openings manifestly afford facilities

for the entry of cold air, so that although this method of protecting

generator-houses has proved efficient in many places, it can only be

considered inferior to the plan of installing a proper heating

arrangement. Occasionally, where local regulations do not forbid, the

entire generator-house may be built as a "lean-to" against some brick

wall which happens to be kept constantly warm, say by having a furnace or

a large kitchen stove on its other side.

In less complicated installations, where there are only two distinct

items in the plant to be protected from frost--generator and holder--or

where generator and holder are combined into one piece of apparatus,

other methods of warming become possible. As the reaction between calcium

carbide and water evolves much heat, the most obvious way of preventing

the plant from freezing is to economise that heat, _i.e._, to retain

as much of it as is necessary within the apparatus. Such a process,

clearly, is only available if the plant is suitable in external form, is

practically self-contained, and comprises no isolated vessels containing

an aqueous liquid. It is indicated, therefore, rather for carbide-to-

water generators, or for water-to-carbide apparatus in which the carbide

chambers are situated inside the main water reservoir--any apparatus, in

fact, where much water is present and where it is all together in one

receptacle. Moreover, the method of heat economy is suited for

application to automatic generators rather than to those belonging to the

opposite system, because automatic apparatus will be generating gas, and

consequently evolving heat, every evening till late at night--just at the

time when frost begins to be severe. A non-automatic generator will

usually be at work only in the mornings, and its store of heat will

accordingly be much more difficult to retain till nightfall. With the

object of storing up the heat evolved in the generator, it must be

covered with some material possessed of the lowest heat-conducting power

possible; and the proper positions for that material in order of

decreasing importance are the top, sides, and bottom of the plant. The

generator may either be covered with a thick layer of straw, carpet,

flannel, or the like, as is done in the protection of exposed water-

pipes; or it may be provided with a jacket filled with some liquid. In

view of the advisability of not having any organic or combustible

material near the generator, the solid substances just mentioned may

preferably be replaced by one of those partially inorganic compositions

sold for "lagging" steam-pipes and engine-cylinders, such as "Fossil

meal." Indeed, the exact nature of the lagging matters comparatively

little, because the active substance in retaining the heat in the

acetylene generator or the steam-pipe is the air entangled in the pores

of the lagging; and therefore the value of any particular material

depends mainly on its exhibiting a high degree of porosity. The idea of

fitting a water jacket round an acetylene generator is not altogether

good, but it may be greatly improved upon by putting into the jacket a

strong solution of some cheap saline body which has the property of

separating from its aqueous solution in the form of crystals containing

water of crystallisation, and of evolving much heat in so separating.

This method of storing much heat in a small space where a fire cannot be

lighted is in common use on some railways, where passengers' foot-warmers

are filled with a strong solution of sodium acetate. When sodium acetate

is dissolved in water it manifestly exists in the liquid state, and it is

presumably present in its anhydrous condition (i.e., not combined with

water of crystallisation). The common crystals are solid, and contain 3

molecules of water of crystallisation--also clearly in the solid state.

Now, the reaction

NaC_2H_3O_2 + 3H_2O = NaC_2H_3O_2.3H_2O

(anhydrous acetate) (crystals)

evolves 4.37 calories (Berthelot), or 1.46 calorie for each molecule of

water; and whereas 1 kilo. of water only evolves 1 large calorie of heat

as its temperature falls 1° C., 18 grammes of water (1 gramme-molecule)

evolve l.46 large calorie when they enter into combination with anhydrous

sodium acetate to assist in forming crystals--and this 1.46 calorie may

either be permitted to warm the mass of crystals, or made to do useful

work by raising the temperature of some adjacent substance. Sodium

acetate crystals dissolve in 3.9 parts by weight of water at 6° C. (43°

F.) or in 2.4 parts at 37° C. (99° F.). If, then, a jacket round an

acetylene apparatus is filled with a warm solution of sodium acetate

crystals in (say) 3 parts by weight of water, the liquid will crystallise

when it reaches some temperature between 99° and 43° F.; but when the

generator comes into action, the heat liberated will change the mass of

crystals into a liquid without raising its sensible temperature to

anything like the extent that would happen were the jacket full of simple

water. Not being particularly warm to the touch, the liquefied product in

the jacket will not lose much heat by radiation, &c., into the

surrounding air; but when the water in the generator falls again (after

evolution of acetylene ceases) the contents of the jacket will also cool,

and finally will begin to crystallise once more, passing a large amount

of low-temperature heat into the water of the generator, and safely

maintaining it for long periods of time at a temperature suitable for the

further evolution of gas. Like the liquid in the seal of an isolated

gasholder, the liquid in such a jacket will last indefinitely; and

therefore the cost of the sodium acetate in negligible.

Another method of keeping warm the water in any part of an acetylene

installation consists in piling round the apparatus a heap of fresh

stable manure, which, as is well known, emits much heat as it rots. Where

horses are kept, such a process may be said to cost nothing. It has the

advantage over methods of lagging or jacketing that the manure can be

thrown over any pipe, water-seal, washing apparatus, &c., even if the

plant is constructed in several separate items. Unfortunately the ammonia

and the volatile organic compounds which are produced during the natural

decomposition of stable manure tend seriously to corrode iron and steel,

and therefore this method of protecting an apparatus from frost should

only be employed temporarily in times of emergency.

CORROSION IN APPARATUS.--All natural water is a solution of oxygen and

may be regarded also as a weak solution of the hypothetical carbonic

acid. It therefore causes iron to rust more or less quickly; and since no

paint is absolutely waterproof, especially if it has been applied to a

surface already coated locally with spots of rust, iron and steel cannot

be perfectly protected by its aid. More particularly at a few inches

above and below the normal level of the water in a holder, therefore, the

metal soon begins to exhibit symptoms of corrosion which may eventually

proceed until the iron is eaten away or becomes porous. One method of

prolonging the life of such apparatus is to give it fresh coats of paint

periodically; but unless the old layers are removed where they have

cracked or blistered, and the rust underneath is entirely scraped off

(which is practically impossible), the new paint films will not last very

long. Another more elegant process for preserving any metal like iron

which is constantly exposed to the attack of a corrosive liquid, and

which is readily applicable to acetylene holders and their tanks, depends

on the principle of galvanic action. When two metals in good electrical

contact are immersed in some liquid that is capable of attacking both,

only that metal will be attacked which is the more electro-positive, or

which (the same thing in other words) is the more readily attacked by the

liquid, evolving the more heat during its dissolution. As long as this

action is proceeding, as long, that is, as some of the more electro-

positive material is present, the less electro-positive material will not

suffer. All that has to be done, therefore, to protect the walls of an

acetylene-holder tank and the sides of its bell is to hang in the seal,

supported by a copper wire fastened to the tank walls by a trustworthy

electrical joint (soldering or riveting it), a plate or rod of some more

electro-positive metal, renewing that plate or rod before it is entirely

eaten away. [Footnote: Contact between the bell and the rod may be

established by means of a flexible metallic wire; or a separate rod might

be used for the bell itself.] If the iron is bare or coated with lead

(paint may be overlooked), the plate may be zinc; if the iron is

galvanised, _i.e._, coated with zinc, the plate may be aluminium or

an alloy of aluminium and zinc. The joint between the copper wire and the

zinc or aluminium plate should naturally be above the water-level. The

foregoing remarks should be read in conjunction with what was said in

Chapter II., about the undesirability of employing a soft solder

containing lead in the construction of an acetylene generator. Here it is

proposed intentionally to set up a galvanic couple to prevent corrosion;

there, with the same object in view, the avoidances of galvanic action is

counselled. The reason for this difference is self-evident; here a

foreign metal is brought into electrical contact with the apparatus in

order that the latter may be made electro-negative; but when a joint is

soldered with lead, the metal of the generator is unintentionally made

electro-positive. Here the plant is protected by the preferential

corrosion of a cheap and renewable rod; in the former case the plant is

encouraged to rust by the unnecessary presence of an improperly selected

metal.

OTHER ITEMS IN GENERATING PLANT.--It has been explained in Chapter II.

that the reaction between calcium carbide and water is very tumultuous in

character, and that it occurs with great rapidity. Clearly, therefore,

the gas comes away from the generator in rushes, passing into the next

item of the plant at great speed for a time, and then ceasing altogether.

The methods necessarily adopted for purifying the crude gas are treated

of in Chapter V.; but it is manifest now that no purifying material can

prove efficient unless the acetylene passes through it at a uniform rate,

and at one which is as slow as other conditions permit. For this reason

the proper position of the holder in an acetylene installation is before

the purifier, and immediately after the condenser or washer which adjoins

the generator. By this method of design the holder is filled up

irregularly, the gas passing into it sometimes at full speed, sometimes

at an imperceptible rate; but if the holder is well balanced and guided

this is a matter of no consequence. Out of the holder, on the other hand,

the gas issues at a rate which is dependent upon the number and capacity

of the burners in operation at any moment; and in ordinary conditions

this rate is so much more uniform during the whole of an evening than the

rate at which the gas is evolved from the carbide, that a purifier placed

after the holder is given a far better opportunity of extracting the

impurities from the acetylene than it would have were it situated before

the holder, as is invariably the case on coal-gas works.

For many reasons, such as capacity for isolation when being recharged or

repaired, it is highly desirable that each item in an acetylene plant

shall be separated, or capable of separation, from its neighbours; and

this observation applies with great force to the holder and the

decomposing vessel of the generator. In all large plants each vessel

should be fitted with a stopcock at its inlet and, if necessary, one at

its outlet, being provided also with a by-pass so that it can be thrown

out of action without interfering with the rest of the installation. In

the best practice the more important vessels, such as the purifiers, will

be in duplicate, so that unpurified gas need not be passed into the

service while a solitary purifier is being charged afresh. In smaller

plants, where less skilled labour will probably be bestowed on the

apparatus, and where hand-worked cocks are likely to be neglected or

misused, some more, automatic arrangement for isolating each item is

desirable. There are two automatic devices which may be employed for the

purposes in view, the non-return valve and the water-seal. The non-return

valve is simply a mushroom or ball valve without handle, lifted off its

seat by gas passing from underneath whenever the pressure of the gas

exceeds the weight of the valve, but falling back on to its seat and

closing the pipe when the pressure decreases or when pressure above is

greater than that below. The apparatus works perfectly with a clean gas

or liquid which is not corrosive; but having regard to the possible

presence of tarry products, lime dust, or sludge, condensed water loaded

with soluble impurities, &c., in the acetylene, a non-return valve is not

the best device to adopt, for both it and the hand-worked cock or screw-

down valve are liable to stick and give trouble. The best arrangement in

all respects, especially between the generator and the holder, is a

water-seal. A water-seal in made by leading the mouth of a pipe

delivering gas under the level of water in a suitable receptacle, so that

the issuing gas has to bubble through the liquid. Gas cannot pass

backwards through the pipe until it has first driven so much liquid

before it that the level in the seal has fallen below the pipe's mouth;

and if the end of the pipe is vertical more pressure than can possibly be

produced in the apparatus is necessary to effect this. Omitting the side

tube _b_, one variety of water-seal is shown at D in Fig. 7 on page

103. The water being at the level _l_, gas enters at _a_ and

bubbles through it, escaping from the apparatus at _c_. It cannot

return from _c_ to _a_ without driving the water out of the

vessel till its level falls from _f_ to _g_; and since the area

of the vessel is much greater than that of the pipe, so great a fall in

the vessel would involve a far greater rise in _a_. It is clear that

such a device, besides acting as a non-return valve, also fulfils two

other useful functions: it serves to collect and retain all the liquid

matter that may be condensed in the pipe _a_ from the spot at which

it was originally level or was given a fall to the seal, as well as that

condensing in _c_ as far as the spot where _c_ dips again; and

it equally acts as a washer to the gas, especially if the orifice

_g_ of the gas-inlet pipe is not left with a plain mouth as

represented in the figure, but terminates in a large number of small

holes, the pipe being then preferably prolonged horizontally, with minute

holes in it so as to distribute the gas throughout the entire vessel.

Such an apparatus requires very little attention. It may with advantage

be provided with the automatic arrangement for setting the water-level

shown at _d_ and _e_. _d_ is a tunnel tube extending

almost to the bottom of the vessel, and _e_ is a curved run-off pipe

of the form shown. The lower part of the upper curve in _e_ is above

the level _f_, being higher than _f_ by a distance equal to

that of the gas pressure in the pipes; and therefore when water is poured

into the funnel it fills the vessel till the internal level reaches

_f_, when the surplus overflows of itself. The operation thus not

only adjusts the quantity of water present to the desired level so that

_a_ cannot become unsealed, but it also renews the liquid when it

has become foul and nearly saturated with dissolved and condensed

impurities from the acetylene. It would be a desirable refinement to give

the bottom of the vessel a slope to the mouth of _e_, or to some

other spot where a large-bore draw-off cock could be fitted for the

purpose of extracting any sludge of lime, &c., that may collect. By

having such a water-seal, or one simpler in construction, between the

generator and the holder, the former may be safely opened at any time for

repairs, inspection, or the insertion of a fresh charge of carbide while

the holder is full of gas, and the delivery of acetylene to the burners

at a specified pressure will not be interrupted. If a cock worked by hand

were employed for the separation of the holder from the generator, and

the attendant were to forget to close it, part or all of the acetylene in

the holder would escape from the generator when it was opened or

disconnected.

Especially when a combined washer and non-return valve follows

immediately after a generator belonging to the shoot type, and the mouth

of the shoot is open to the air in the plant-house, it is highly

desirable that the washer shall be fitted with some arrangement of an

automatic kind for preventing the water level rising much above its

proper position. The liquid in a closed washer tends to rise as the

apparatus remains in use, water vapour being condensed within it and

liquid water, or froth of lime, being mechanically carried forward by the

stream of acetylene coming from the decomposing chamber. In course of

time, therefore, the vertical depth to which the gas-inlet pipe in the

washer is sealed by the liquid increases; and it may well be that

eventually the depth in question, plus the pressure thrown by the holder

bell, may become greater than the pressure which can be set up inside the

generator without danger of gas slipping under the lower edge of the

shoot. Should this state of things arise, the acetylene can no longer

force its way through the washer into the holder bell, but will escape

from the mouth of the shoot; filling the apparatus-house with gas, and

offering every opportunity for an explosion if the attendant disobeys

orders and takes a naked light with him to inspect the plant.

It is indispensable that every acetylene apparatus shall be fitted with a

safety-valve, or more correctly speaking a vent-pipe. The generator must

have a vent-pipe in case the gas-main leading to the holder should become

blocked at any time, and the acetylene which continues to be evolved in

all water-to-carbide apparatus, even after the supply of water has been

cut off be unable to pass away. Theoretically a non-automatic apparatus

does not require a vent-pipe in its generator because all the gas enters

the holder immediately, and is, or should be, unable to return through

the intermediate water seal; practically such a safeguard is absolutely

necessary for the reason given. The holder must have a safety-valve in

case the cutting-off mechanism of the generator fails to act, and more

gas passes into it than it can store. Manifestly the pressure of the gas

in a water-sealed holder or in any generator fitted with a water-sealed

lid cannot rise above that corresponding with the depth of water in the

seal; for immediately the pressure, measured in inches of water, equals

the depth of the sealing liquid, the seal will be blown out, and the gas

will escape. Such an occurrence, however, as the blowing of a seal must

never be possible in any item of an acetylene plant, more especially in

those items that are under cover, for the danger that the issuing gas

might be fired or might produce suffocation would be extremely great.

Typical simple forms of vent-pipe suitable for acetylene apparatus are

shown in Fig. 7. In each case the pipe marked "vent" is the so-called

safety-valve; it is open at its base for the entry of gas, and open at

its top for the escape of the acetylene into the atmosphere, such top

being in all instances carried through the roof of the generator-house

into the open air, and to a spot distant from any windows of that house

or of the residence, where it can prove neither dangerous nor a nuisance

by reason of its odour. At A is represented the vent-pipe of a

displacement vessel, which may either be part of a displacement holder or

of a generator working on the displacement principle. The vent-pipe is

rigidly fixed to the apparatus. If gas is generated within the closed

portion of the holder or passes through it, and if the pressure so set up

remains less than that which is needed to move the water from the level

_l_ to the levels _l'_ and _l"_, the mouth of the pipe is

under water, and acetylene cannot enter it; but immediately such an

amount of gas is collected, or such pressure is produced that the

interior level sinks below _l"_, which is that of the mouth of the

pipe, it becomes unsealed, and the surplus gas freely escapes. There are

two minor points in connexion with this form of vent-pipe often

overlooked. At the moment when the water arrives at _l"_ in the

closed half of the apparatus, its level in the interior of the vent-pipe

stands at _l'_, identical with that in the open hall of the

apparatus (for the mouth of the vent-pipe and the water in the open hall

of the apparatus are alike exposed to the pressure of the atmosphere

only). When the water, then, descends just below _l"_ there is an

amount of water inside the pipe equal in height to the distance between

_l'_ and _l"_; and before the acetylene can escape, it must

either force this water as a compact mass out of the upper mouth of the

vent-pipe (which it is clearly not in a position to do), drive it out of

the upper mouth a little at a time, or bubble through it till the water

is gradually able to run downwards out of the pipe as its lower opening

is more fully unsealed. In practice the acetylene partly bubbles through

this water and partly drives it out of the mouth of the pipe; on some

occasions temporarily yielding irregular pressures at the burners which

cause them to jump, and always producing a gurgling noise in the vent-

pipe which in calculated to alarm the attendant. If the pipe is too small

in diameter, and especially if its lower orifice is cut off perfectly

horizontal and constricted slightly, the water may refuse to escape from

the bottom altogether, and the pipe will fail to perform its allotted

task. It is better therefore to employ a wide tube, and to cut off its

mouth obliquely, or to give its lower extremity the shape of an inverted

funnel. At the half of the central divided drawing marked B (Fig. 7) is

shown a precisely similar vent-pipe affixed to the bell of a rising

holder, which behaves in an identical fashion when by the rising of the

bell its lower end is lifted out of the water in the tank. The features

described above as attendant, upon the act of unsealing of the

displacement-holder vent-pipe occur here also, but to a less degree; for

the water remaining in the pipe at the moment of unsealing is only that

which corresponds with the vertical distance between _l'_ and

_l"_, and in a rising holder this is only a height always equal to

the pressure given by the bell. Nevertheless this form of vent-pipe

produces a gurgling noise, and would be better for a trumpet-shaped

mouth. A special feature of the pipe in B is that unless it is placed

symmetrically about the centre of the bell its weight tends to throw the

bell out of the vertical, and it may have to be supported at its upper

part; conversely, if the pipe is arranged concentrically in the bell, it

may be employed as part of the guiding arrangement of the bell itself.

Manifestly, as the pipe must be long enough to extend through the roof of

the generator-house, its weight materially increases the weight of the

bell, and consequently the gas pressure in the service; this fact is not

objectionable provided due allowance is made for it. So tall a vent-pipe,

however, seriously raises the centre of gravity of the bell and may make

it top-heavy. To work well the centre of gravity of a holder bell should

be as low as possible, any necessary weighting being provided

symmetrically about its circumference and close to its bottom edge. The

whole length of an ascending vent-pipe need not be carried by the rising

bell, because the lower portion, which must be supported by the bell, can

be arranged to slide inside a wider length of pipe which is fixed to the

roof of the generator-house at the point where it passes into the open

air.

[Illustration: FIG. 7.--TYPICAL FORMS OF VENT-PIPES OR SAFETY-VALVES.]

A refinement upon this vent-pipe is represented at C, where it is rigidly

fastened to the tank of the holder, and has its internal aperture always

above the level of the water in the apparatus. Rigidly fixed to the crown

of the bell is a tube of wider diameter, _h_, which is closed at its

upper end. _h_ is always full of gas, and its mouth is normally

beneath the level of the water in the seal; but when the bell rises to

its highest permissible position, the mouth of _h_ comes above the

water, and communication is opened between the holder and the outer

atmosphere. No water enters the vent-pipe from the holder, and therefore

no gurgling or irregular pressure is produced. Another excellent

arrangement of a vent-pipe, suggested by Klinger of Gumpoldskirchen, is

shown at D, a drawing which has already been partly considered as a

washer and water-seal. For the present purpose the main vessel and its

various pipes are so dimensioned that the vertical height _g_ to

_f_ is always appreciably greater than the gas pressure in the

service or in the generator or gasholder to which it is connected. In

these circumstances the gas entering at _a_ depresses the water in

the pipe below the level _f_ to an extent equal to the pressure at

which it enters that pipe--an extent normally less than the distance

_f_ to _g_; and therefore gas never passes into the body of the

vessel, but travels away by the side tube _b_ (which in former

references to this drawing was supposed to be absent). If, however, the

pressure at _a_ exceeds that of the vertical height _f_ to

_g_, gas escapes at _g_ through the water, and is then free to

reach the atmosphere by means of the vent _c_. As before, _d_

serves to charge the apparatus with water, and _e_ to ensure a

proper amount being added. Clearly no liquid can enter the vent-pipe in

this device. Safety-valves such as are added to steam-boilers and the

like, which consist of a weighted lever holding a conical valve down

against its seat, are not required in acetylene apparatus, for the

simpler hydraulic seals discussed above can always be fitted wherever

they may be needed. It should be noticed that these vent-pipes only come

into operation in emergencies, when they are required to act promptly. No

economy is to be effected by making them small in diameter. For obvious

reasons the vent-pipe of a holder should have a diameter equal to that of

the gas-inlet tube, and the vent-pipe of a generator be equal in size to

the gas-leading tube.

FROTHING IN GENERATORS.--A very annoying trouble which crops up every now

and then during the evolution of acetylene consists in the production of

large masses of froth within the generator. In the ordinary way,

decomposition of carbide is accompanied by a species of effervescence,

but the bubbles should break smartly and leave the surface of the liquid

reasonably free from foam. Sometimes, however, the bubbles do not break,

but a persistent "head" of considerable height is formed. Further

production of gas only increases the thickness of the froth until it

rises so high that it is carried forward through the gas-main into the

next item of the plant. The froth disappears gradually in the pipes, but

leaves in them a deposit of lime which sooner or later causes

obstructions by accumulating at the angles and dips; while during its

presence in the main the steady passage of gas to the holder is

interrupted and the burners may even be made to jump. Manifestly the

defect is chiefly, if not always, to be noticed in the working of

carbide-to-water generators. The phenomenon has been examined by

Mauricheau-Beaupré, who finds that frothing is not characteristic of pure

carbide and that it cannot be attributed to any of the impurities

normally present in commercial carbide. If, however, the carbide contains

calcium chloride, frothing is liable to occur. A 0.1 per cent. solution

of calcium chloride appears to yield some foam when carbide is decomposed

in it, and a 1 per cent. solution to foam in a pronounced manner. In the

absence of calcium chloride, the main cause of frothing seems to be the

presence in the generator of new paint or tar. If a generator is taken

into use before the paint in any part of it which becomes moistened by

warm lime-water has had opportunity of drying thoroughly hard, frothing

is certain to occur; and even if the carbide has been stored for only a

short time in a tin or drum which has been freshly painted, a production

of froth will follow when it is decomposed in water. The products of the

polymerisation of acetylene also tend to produce frothing, but not to

such an extent as the turpentine in paint and the lighter constituents of

coal-tar. Carbide stored even temporarily in a newly painted tin froths

on decomposition because it has absorbed among its pores some of the

volatile matter given off by the paint during the process of desiccation.

THE "DRY" PROCESS OF GENERATION.--A process for generating acetylene,

totally different in principle from those hitherto considered, has been

introduced in this country. According to the original patents of G. J.

Atkins, the process consisted in bringing small or powdered carbide into

mechanical contact with some solid material containing water, the water

being either mixed with the solid reagent or attached to it as water of

crystallisation. Such reagents indeed were claimed as crude starch and

the like, the idea being to recover a by-product of pecuniary value. Now

the process seems to be known only in that particular form in which

granulated carbide is treated with crystallised sodium carbonate,

_i.e._, common washing soda. Assuming the carbide employed to be

chemically pure and the reaction between it and the water of

crystallisation contained in ordinary soda crystals to proceed

quantitatively, the production of acetylene by the dry process should be

represented by the following chemical equation:

5CaC_2 + Na_2CO_3.10H_2O = 5C_2H_2 + 5Ca(OH)_2 + Na_2CO_3.

On calculating out the molecular weights, it will be seen that 286 parts

of washing soda should suffice for the decomposition of 320 parts of pure

calcium carbide, or in round numbers 9 parts of soda should decompose 10

parts of carbide. In practice, however, it seems to be found that from 1

to 1.5 parts of soda are needed for every part of carbide.

The apparatus employed is a metal drum supported on a hollow horizontal

spindle, one end of which is closed and carries a winch handle, and the

other end of which serves to withdraw the gas generated in the plant. The

drum is divided into three compartments by means of two vertical

partitions so designed that when rotation proceeds in one particular

direction portions of the two reagents stored in one end compartment pass

into the centre compartment; whereas when rotation proceeds in the

opposite direction, the material in the centre compartment is merely

mixed together, partly by the revolution of the drum, partly with the

assistance of a stationary agitator slung loosely from the central

spindle. The other end compartment contains coke or sawdust or other dry

material through which the gas passes for the removal of lime or other

dust carried in suspension as it issues from the generating compartment.

The gas then passes through perforations into the central spindle, one

end of which is connected by a packed joint with a fixed pipe, which

leads to a seal or washer containing petroleum. Approached from a

theoretical standpoint, it will be seen that this method of generation

entirely sacrifices the advantages otherwise accruing from the use of

liquid water as a means for dissipating the heat of the chemical

reaction, but on the other hand, inasmuch as the substances are both

solid, the reaction presumably occurs more slowly than it would in the

presence of liquid water; and moreover the fact that the water employed

to act upon the carbide is in the solid state and also more or less

combined with the rest of the sodium carbonate molecule, means that, per

unit of weight, the water decomposed must render latent a larger amount

of heat than it would were it liquid. Experiments made by one of the

authors of this book tend to show that the gas evolved from carbide by

the dry process contains rather less phosphorus than it might in other

conditions of generation, and as a fact gas made by the dry process is

ordinarily consumed without previous passage through any chemical

purifying agent. It is obvious, however, that the use of the churn

described above greatly increases the labour attached to the production

of the gas; while it is not clear that the yield per unit weight of

carbide decomposed should be as high as that obtained in wet generation.

The inventor has claimed that his by-product should be valuable and

saleable, apparently partly on the ground that it should contain caustic

soda. Evidence, however, that a reaction between the calcium oxide or

hydroxide and the sodium carbonate takes place in the prevailing

conditions is not yet forthcoming, and the probabilities are that such

decomposition would not occur unless the residue were largely diluted

with water. [Footnote: The oldest process employed for manufacturing

caustic soda consisted in mixing a solution of sodium carbonate with

quick or slaked lime, and it has been well established that the

causticisation of the soda will not proceed when the concentration of the

liquid is greater than that corresponding with a specific gravity of

about 1-10, _i.e._, when the liquid contains more than some 8 to 10

per cent, of sodium hydroxide.] Conversely there are some grounds for

believing that the dry residue is less useful than an ordinary wet

residue for horticultural purposes, and also for the production of

whitewash. From a financial standpoint, the dry process suffers owing to

the expense involved in the purchase of a second raw material, for which

but little compensation can be discovered unless it is proved that the

residue is intrinsically more valuable than common acetylene-lime and can

be sold or used advantageously by the ordinary owner of an installation.

The discarding of the chemical purifier at the present day is a move of

which the advantage may well be overrated.

ARTIFICIAL LIGHTING OF GENERATOR SHEDS.--It has already been argued that

all normal or abnormal operations in connexion with an acetylene

generating plant should be carried out, if possible, by daylight; and it

has been shown that on no account must a naked light ever be taken inside

the house containing such a plant. It will occasionally happen, however,

that the installation must be recharged or inspected after nightfall. In

order to do this in safety, a double window, incapable of being opened,

should be fitted in one wall of the house, as far as possible from the

door, and in such a position that the light may fall on to all the

necessary places. Outside this window may be suspended an ordinary hand-

lantern burning oil or paraffin; or, preferably, round this window may be

built a closed lantern into which some source of artificial light may be

brought. If the acetylene plant has an isolated holder of considerable

size, there is no reason at all why a connexion should not be made with

the service-pipes, and an acetylene flame be used inside this lantern;

but with generators of the automatic variety, an acetylene light is not

so suitable, because of the fear that gas may not be available precisely

at the moment when it is necessary to have light in the shed. It would,

however, be a simple matter to erect an acetylene burner inside the

lantern in such a way that when needed an oil-lamp or candle could be

used instead. Artificial internal light of any kind is best avoided; the

only kind permissible being an electric glow-lamp. If this is employed,

it should be surrounded by a second bulb or gas-tight glass jacket, and

preferably by a wire cage as well; the wires leading to it must be

carefully insulated, and all switches or cut-outs (which may produce a

spark) must be out of doors. The well-known Davy safety or miner's lamp

is not a trustworthy instrument for use with acetylene because of

(_a_) the low igniting-point of acetylene; (_b_) the high

temperature of its flame; and (_c_) the enormous speed at which the

explosive wave travels through a mixture of acetylene and air. For these

reasons the metallic gauze of the Davy lamp is not so efficient a

protector of the flame as it is in cases of coal-gas, methane, &c.

Moreover, in practice, the Davy lamp gives a poor light, and unless in

constant use is liable to be found out of order when required. It should,

however, be added that modern forms of the safety lamp, in which the

light is surrounded by a stout glass chimney and only sufficient gauze is

used for the admission of fresh air and for the escape of the combustion

products, appear quite satisfactory when employed in an atmosphere

containing some free acetylene.

CHAPTER IV

THE SELECTION OF AN ACETYLENE GENERATOR

In Chapter II. an attempt has been made to explain the physical and

chemical phenomena which accompany the interaction of calcium carbide and

water, and to show what features in the reaction are useful and what

inconvenient in the evolution of acetylene on a domestic or larger scale.

Similarly in Chapter III. have been described the various typical devices

which may be employed in the construction of different portions of

acetylene plant, so that the gas may be generated and stored under the

best conditions, whether it is evolved by the automatic or by the non-

automatic system. This having been done, it seemed of doubtful utility to

include in the first edition of this work a long series of illustrations

of such generators as had been placed on the markets by British, French,

German, and American makers. It would have been difficult within

reasonable limits to have reproduced diagrams of all the generators that

had been offered for sale, and absolutely impossible within the limits of

a single hand-book to picture those which had been suggested or patented.

Moreover, some generating apparatus appeared on the market ephemerally;

some was constantly being modified in detail so as to alter parts which

experience or greater knowledge had shown the makers to be in need of

alteration, while other new apparatus was constantly being brought out.

On these and other grounds it did not appear that much good purpose would

have been served by describing the particular apparatus which at that

time would have been offered to prospective purchasers. It seemed best

that the latter should estimate the value and trustworthiness of

apparatus by studying a section of it in the light of the general

principles of construction of a satisfactory generator as enunciated in

the book. While the position thus taken by the authors in 1903 would

still not be incorrect, it has been represented to them that it would

scarcely be inconsistent with it to give brief descriptions of some of

the generators which are now being sold in Great Britain and a few other

countries. Six more years' experience in the design and manufacture of

acetylene plant has enabled the older firms of manufacturers to fix upon

certain standard patterns for their apparatus, and it may confidently be

anticipated that many of these will survive a longer period. Faulty

devices and designs have been weeded out, and there are lessons of the

past as well as theoretical considerations to guide the inventor of a new

type of generator. On those grounds, therefore, an attempt has now been

made to give brief descriptions, with sectional views, of a number of the

generators now on the market in Great Britain. Moreover, as the first

edition of this book found many readers in other countries, in several of

which there is greater scope for the use of acetylene, it has been

decided to describe also a few typical or widely used foreign generators.

All the generators described must stand or fall on their merits, which

cannot be affected by any opinion expressed by the authors. In the

descriptions, which in the first instance have generally been furnished

by the manufacturers of the apparatus, no attempt has therefore been made

to appraise the particular generators, and comparisons and eulogistic

comments have been excluded. The descriptions, however, would

nevertheless have been somewhat out of place in the body of this book;

they have therefore been relegated to a special Appendix. It has, of

course, been impossible to include the generators of all even of the

English manufacturers, and doubtless many trustworthy ones have remained

unnoticed. Many firms also make other types of generators in addition to

those described. It must not be assumed that because a particular make of

generator is not mentioned it is necessarily faulty. The apparatus

described may be regarded as typical or well known, and workable, but it

is not by reason of its inclusion vouched for in any other respect by the

authors. The Appendix is intended, not to bias or modify the judgment of

the would-be purchaser of a generator, but merely to assist him in

ascertaining what generators there are now on the market.

The observations on the selection of a generator which follow, as well as

any references in other chapters to the same matter, have been made

without regard to particular apparatus of which a description may (or may

not) appear in the Appendix. With this premise, it may be stated that the

intending purchaser should regard the mechanism of a generator as shown

in a sectional view or on inspection of the apparatus itself. If the

generator is simple in construction, he should be able to understand its

method of working at a glance, and by referring it to the type

(_vide_ Chapter III.) to which it belongs, be able to appraise its

utility from a chemical and physical aspect from what has already been

said. If the generator is too complicated for ready understanding of its

mode of working, it is not unlikely to prove too complicated to behave

well in practice. Not less important than the mechanism of a generator is

good construction from the mechanical point of view, _i.e._, whether

stout metal has been employed, whether the seams and joints are well

finished, and whether the whole apparatus has been built in the workman-

like fashion which alone can give satisfaction in any kind of plant.

Bearing these points in mind, the intending purchaser may find assistance

in estimating the mechanical value of an apparatus by perusing the

remainder of this chapter, which will be devoted to elaborating at length

the so-called scientific principles underlying the construction of a

satisfactory generator, and to giving information on the mechanical and

practical points involved.

It is perhaps desirable to remark that there is scarcely any feature in

the generation of acetylene from calcium carbide and water--certainly no

important feature--which introduces into practice principles not already

known to chemists and engineers. Once the gas is set free it ranks simply

as an inflammable, moisture-laden, somewhat impure, illuminating and

heat-giving gas, which has to be dried, purified, stored, and led to the

place of combustion; it is in this respect precisely analogous to coal-

gas. Even the actual generation is only an exothermic, or heat-producing,

reaction between a solid and a liquid, in which rise of temperature and

pressure must be prevented as far as possible. Accordingly there is no

fundamental or indispensable portion of an acetylene apparatus which

lends itself to the protection of the patent laws; and even the details

(it may be said truthfully, if somewhat cynically) stand in patentability

in inverse ratio to their simplicity and utility.

During the early part of 1901 a Committee appointed by the British Home

Office, "to advise as to the conditions of safety to which acetylene

generators should conform, and to carry out tests of generators in the

market in order to ascertain how far those conform with such conditions,"

issued a circular to the trade suggesting that apparatus should be sent

them for examination. In response, forty-six British generators were

submitted for trial, and were examined in a fashion which somewhat

exceeded the instructions given to the Committee, who finally reported to

the Explosives Department of the Home Office in a Blue Book, No. Cd. 952,

which can be purchased through any bookseller. This report comprises an

appendix in which most of the apparatus are illustrated, and it includes

the result of the particular test which the Committee decided to apply.

Qualitatively the test was useful, as it was identical in all instances,

and only lacks full utility inasmuch as the trustworthiness of the

automatic mechanism applied to such generators as were intended to work

on the automatic system was not estimated. Naturally, a complete

valuation of the efficiency of automatic mechanism cannot be obtained

from one or even several tests, it demands long-continued watching; but a

general notion of reliability might have been obtained. Quantitatively,

however, the test applied by the Committee is not so free from reproach,

for, from the information given, it would appear to have been less fair

to some makers of apparatus than to others. Nevertheless the report is

valuable, and indicates the general character of the most important

apparatus which were being offered for sale in the United Kingdom in

1900-1901.

It is not possible to give a direct answer to the question as to which is

the best type of acetylene generator. There are no generators made by

responsible firms at the present time which are not safe. Some may be

easier to charge and clean than others; some require more frequent

attention than others; some have moving parts less likely to fail, when

handled carelessly, than others; some have no moving mechanism to fail.

For the illumination of a large institution or district where one man can

be fully occupied in attending to the plant, cleaning, lighting, and

extinguishing the lamps, or where other work can be found for him so as

to leave him an hour or so every day to look after the apparatus, the

hand-fed carbide-to-water generator L (Fig. 6) has many advantages, and

is probably the best of all. In smaller installations choice must be made

first between the automatic and the non-automatic principle--the

advantages most frequently lying with the latter. If a non-automatic

generator is decided upon, the hand carbide-feed or the flooded-

compartment apparatus is almost equally good; and if automatism is

desired, either a flooded-compartment machine or one of the most

trustworthy types of carbide-feed apparatus may be taken. There are

contact apparatus on the markets which appear never to have given

trouble, and those are worthy of attention. Some builders advocate their

own apparatus because the residue is solid and not a cream. If there is

any advantage in this arising from greater ease in cleaning and

recharging the generator and in disposing of the waste, that advantage is

usually neutralised by the fear that the carbide may not have been wholly

decomposed within the apparatus; and whereas any danger arising from

imperfectly spent carbide being thrown into a closed drain may be

prevented by flooding the residue with plenty of water in an open vessel,

imperfect decomposition in the generator means a deficiency in the amount

of gas evolved from a unit weight of solid taken or purchased. In fact,

setting on one side apparatus which belong to a notoriously defective

system and such as are constructed in large sizes on a system that is

only free from overheating, &c., in small sizes; setting aside all

generators which are provided with only one decomposing chamber when they

are of a capacity to require two or more smaller ones that can more

efficiently be cooled with water jackets; and setting aside any form of

plant which on examination is likely to exhibit any of the more serious

objections indicated in this and the previous chapters, there is

comparatively little to choose, from the chemical and physical points of

view, between the different types of generators now on the markets. A

selection may rather be made on mechanical grounds. The generator must be

well able to produce gas as rapidly as it will ever be required during

the longest or coldest evening; it must be so large that several more

brackets or burners can be added to the service after the installation is

complete. It must be so strong that it will bear careless handling and

the frequent rough manipulation of its parts. It must be built of stout

enough material not to rust out in a few years. Each and all of its parts

must be accessible and its exterior visible. Its pipes, both for gas and

sludge, must be of large bore (say 1 inch), and fitted at every dip with

an arrangement for withdrawing into some closed vessel the moisture, &c.,

that may condense. The number of cocks, valves, and moving parts must be

reduced to a minimum; cocks which require to be shut by hand before

recharging must give way to water-seals. It must be simple in all its

parts, and its action intelligible at a glance. It must be easy to

charge--preferably even by the sense of touch in darkness. It must be

easy to clean. The waste lime must be easily removed. It must be so

fitted with vent-pipes that the pressure can never rise above that at

which it is supposed to work. Nevertheless, a generator in which these

vent-pipes are often brought into use is badly constructed and wasteful,

and must be avoided. The water of the holder seal should be distinct from

that used for decomposing the carbide; and those apparatus where the

holder is entirely separated from the generator are preferable to such as

are built all in one, even if water-seals are fitted to prevent return of

gas. Apparatus which is supposed to be automatic should be made perfectly

automatic, the water or the carbide-feed being locked automatically

before the carbide store, the decomposing chamber, or the sludge-cock can

be opened. The generating chamber must always be in communication with

the atmosphere through a water-sealed vent-pipe, the seal of which, if

necessary, the gas can blow at any time. All apparatus should be fitted

with rising holders, the larger the better. Duplicate copies of printed

instructions should be demanded of the maker, one copy being kept in the

generator-house, and the other elsewhere for reference in emergencies.

These instructions must give simple and precise information as to what

should be done in the event of a breakdown as well as in the normal

manipulation of the plant. Technical expressions and descriptions of

parts understood only by the maker must be absent from these rules.

ADDENDUM.

BRITISH AND FOREIGN REGULATIONS FOR THE CONSTRUCTION AND INSTALLATION OF

ACETYLENE GENERATING PLANT

Dealing with the "conditions which a generator should fulfil before it

can be considered as being safe," the HOME OFFICE COMMITTEE of 1901

before mentioned write as follows:

1. The temperature in any part of the generator, when run at the maximum

rate for which it is designed, for a prolonged period, should not exceed

130° C. This may be ascertained by placing short lengths of wire, drawn

from fusible metal, in those parts of the apparatus in which heat is

liable to be generated.

2. The generator should have an efficiency of not less than 90 per cent.,

which, with carbide yielding 5 cubic feet per pound, would imply a yield

of 4.5 cubic feet for each pound of carbide used.

3. The size of the pipes carrying the gas should be proportioned to the

maximum rate of generation, so that undue back pressure from throttling

may not occur.

4. The carbide should be completely decomposed in the apparatus, so that

lime sludge discharged from the generator shall not be capable of

generating more gas.

5. The pressure in any part of the apparatus, on the generator side of

the holder, should not exceed that of 20 inches of water, and on the

service side of same, or where no gasholder is provided, should not

exceed that of 5 inches of water.

6. The apparatus should give no tarry or other heavy condensation

products from the decomposition of the carbide.

7. In the use of a generator regard should be had to the danger of

stoppage of passage of the gas and resulting increase of pressure which

may arise from the freezing of the water. Where freezing may be

anticipated, steps should be taken to prevent it.

8. The apparatus should be so constructed that no lime sludge can gain

access to any pipes intended for the passage of gas or circulation of

water.

9. The use of glass gauges should be avoided as far as possible, and,

where absolutely necessary, they should be effectively protected against

breakage.

10. The air space in a generator before charging should be as small as

possible.

11. The use of copper should be avoided in such parts of the apparatus as

are liable to come in contact with acetylene.

The BRITISH ACETYLENE ASSOCIATION has drawn up the following list of

regulations which, it suggests, shall govern the construction of

generators and the installation of piping and fittings:

1. Generators shall be so constructed that, when used in accordance with

printed instructions, it shall not be possible for any undecomposed

carbide to remain in the sludge removed therefrom.

2. The limit of pressure in any part of the generator shall not exceed

that of 20 inches of water, subject to the exception that if it be shown

to the satisfaction of the Executive of the Acetylene Association that

higher pressures up to 50 inches of water are necessary in certain

generators, and are without danger, the Executive may, with the approval

of the Home Office, grant exemption for such generators, with or without

conditions.

3. The limit of pressure in service-pipes, within the house, shall not

exceed 10 inches of water.

4. Except when used for special industrial purposes, such as oxy-

acetylene welding, factories, lighthouses, portable apparatus containing

not more than four pounds of carbide, and other special conditions as

approved by the Association, the acetylene plant, such as generators,

storage-holders, purifiers, scrubbers, and for washers, shall be in a

suitable and well-ventilated outhouse, in the open, or in a lean-to,

having no direct communication with a dwelling-house. A blow-off pipe or

safety outlet shall be arranged in such a manner as to carry off into the

open air any overmake of gas and to open automatically if pressure be

increased beyond 20 inches water column in the generating chamber or

beyond 10 inches in the gasholder, or beyond the depth of any fluid seal

on the apparatus.

5. Generators shall have sufficient storage capacity to make a serious

blow-off impossible.

6. Generators and apparatus shall be made of sufficiently strong material

and be of good workmanship, and shall not in any part be constructed of

unalloyed copper.

7. It shall not be possible under any conditions, even by wrong

manipulation of cocks, to seal the generating chamber hermetically.

8. It shall not be possible for the lime sludge to choke any of the gas-

pipes in the apparatus, nor water-pipes if such be alternately used as

safety-valves.

9. In the use of a generator, regard shall be had to the danger of

stoppage of passage of the gas, and resulting increase of pressure, which

may arise from the freezing of the water. Where freezing may be

anticipated, steps shall be taken to prevent it.

10. The use of glass gauges shall be avoided as far as possible, and

where absolutely necessary they shall be effectively protected against

breakage.

11. The air space in the generator before charging shall be as small as

possible, _i.e._, the gas in the generating chamber shall not

contain more than 8 per cent. of air half a minute after commencement of

generation. A sample of the contents, drawn from the holder any time

after generation has commenced, shall not contain an explosive mixture,

_i.e._, more than 18 per cent, of air. This shall not apply to the

initial charges of the gasholder, when reasonable precautions are taken.

12. The apparatus shall produce no tarry or other heavy condensation

products from the decomposition of the carbide.

13. The temperature of the gas, immediately on leaving the charge, shall

not exceed 212° F. (100° C.)

14. No generator shall be sold without a card of instructions suitable

for hanging up in some convenient place. Such instructions shall be of

the most detailed nature, and shall not presuppose any expert knowledge

whatever on the part of the operator.

15. Notice to be fixed on Generator House Door, "NO LIGHTS OR SMOKING

ALLOWED."

16. Every generator shall have marked clearly upon the outside a

statement of the maximum number of half cubic foot burners and the charge

of carbide for which it is designed.

17. The Association strongly advise the use of an efficient purifier with

generating plant for indoor lighting.

18. No composition piping shall be used in any part of a permanent

installation.

19. Before being covered in, all pipe-work (main and branches) shall be

tested in the following manner: A special acetylene generator, giving a

pressure of at least 10 inches water column in a gauge fixed on the

furthest point from the generator, shall be connected to the pipe-work.

All points shall be opened until gas reaches them, when they shall be

plugged and the main cock on the permanent generator turned off, but all

intermediate main cocks shall be open in order to test underground main

and all connexions. The gauge must not show a loss after generator has

been turned off for at least two hours.

20. After the fittings (pendants, brackets, &c.) have been fixed and all

burners lighted, the gas shall be turned off at the burners and the whole

installation shall be re-tested, but a pressure of 5 inches shall be

deemed sufficient, which shall not drop lower than to 4-1/2 inches on the

gauge during one hour's test.

21. No repairs to, or alterations in, any part of a generator, purifier,

or other vessel which has contained acetylene shall be commenced, nor,

except for recharging, shall any such part or vessel be cleaned out until

it has been completely filled with water, so as to expel any acetylene or

mixture of acetylene and air which may remain in the vessel, and may

cause a risk of explosion.

_Recommendation_.--It being the general practice to store carbide in

the generator-house, the Association recommend that the carbide shall be

placed on a slightly raised platform above the floor level.

THE BRITISH FIRE OFFICES COMMITTEE in the latest revision, dated July 15,

1907, of its Rules and Regulations _re_ artificial lighting on

insured premises, includes the following stipulations applicable to

acetylene:

Any apparatus, except as below, for generating, purifying, enriching,

compressing or storing gas, must be either in the open or in a building

used for such purposes only, not communicating directly with any building

otherwise occupied.

An acetylene portable apparatus is allowed, provided it holds a charge of

not more than 2 lb. of carbide.

A cylinder containing not more than 20 cubic feet of acetylene compressed

and (or) dissolved in accordance with an Order of Secretary of State

under the Explosives Act, 1875, is allowed.

The use of portable acetylene lamps containing charges of carbide

exceeding the limit of 2 lb. allowed under these Rules (the average

charge being about 18 lb.) is allowed in the open or in buildings in

course of erection.

Liquid acetylene must not be used or stored on the premises.

The pipe, whether flexible or not, connecting an incandescent gas lamp to

the gas-supply must be of metal with metal connexions.

(The reference in these Rules to the storage of carbide has been quoted

in Chapter II. (page 19).)

These rules are liable to revision from time to time.

The GERMAN ACETYLENE VEREIN has drawn up (December 1904) the following

code of rules for the construction, erection, and manipulation of

acetylene apparatus:

I. _Rules for Construction._

1. All apparatus for the generation, purification, and storage of

acetylene must be constructed of sheet or cast iron. Holder tanks may be

built of brick.

2. When bare, galvanised, or lead-coated sheet-iron is used, the sides of

generators, purifiers, condensers, holder tanks, and (if present) washers

and driers must be built with the following gauges as minima:

Holder bells. All other apparatus.

Up to 7 cubic feet capacity 0.75 mm. 1.00 mm.

From 7 to 18 " 1.00 1.25

From 18 to 53 " 1.25 1.50

Above 53 " 1.50 2.00

When not constructed of cast-iron, the bottoms, covers, and "manhole"

lids must be 0.5 mm. thicker in each respective size.

In all circumstances, the thickness of the walls--especially in the case

of apparatus not circular in horizontal section--must be such that

alteration in shape appears impossible, unless deformation is guarded

against in other ways.

Generators must be so constructed that when they are being charged the

carbide cannot fall into the residue which has already been gasified; and

the residues must always be capable of easy, complete, and safe removal.

3. Generators, purifiers, and holders must be welded, riveted or folded

at the seams; soft solder is only permissible as a tightening material.

4. Pipes delivering acetylene, or uniting the apparatus, must be cast- or

wrought-iron. Unions, cocks, and valves must not be made of copper; but

the use of brass and bronze is permitted.

5. When cast-iron is employed, the rules of the German Gas and Water

Engineers are to be followed.

6. In generators where the whole amount of carbide introduced is not

gasified at one time, it must be possible to add fresh water or carbide

in safety, without interfering with the action of the apparatus. In such

generators the size of the gasholder space is to be calculated according

to the quantity of carbide which can be put into the generator. For every

1 kilogramme of carbide the available gasholder space must be: for the

first 50 kilos., 20 litres; for the next 50 kilos., 15 litres; for

amounts above 100 kilos., 10 litres per kilo. [One kilogramme may be

taken as 2.2 lb., and 28 litres as 1 cubic foot.]

The generator must be large enough to supply the full number of normal

(10-litre) burners with gas for 5 hours; the yield of acetylene being

taken at 290 litres per kilo. [4.65 cubic feet per lb.]

The gasholder space of apparatus where carbide is not stored must be at

least 30 litres for every normal (10-litre) flame.

7. The gasholder must be fitted with an appliance for removing any gas

which may be generated (especially when the apparatus is first brought

into action) after the available space is full. This vent must have a

diameter at least equal to the inlet pipe of the holder.

8. Acetylene plant must be provided with purifying apparatus which

contains a proper purifying material in a suitable condition.

9. The dimensions of subsidiary apparatus, such as washers, purifiers,

condensers, pipes, and cocks must correspond with the capacity of the

plant.

10. Purifiers and washers must be constructed of materials capable of

resisting the attack of the substances in them.

11. Every generator must bear a plate giving the name of the maker, or

the seller, and the maximum number of l0-litre lights it is intended to

supply. If all the carbide put into the generator is not gasified at one

time, the plate must also state the maximum weight of carbide in the

charge. The gasholder must also bear a plate recording the maker's or

seller's name, as well as its storage capacity.

12. Rules 1 to 11 do not apply to portable apparatus serving up to two

lights, or to portable apparatus used only out of doors for the lighting

of vehicles or open spaces.

II. _Rules for Erection_

1. Acetylene apparatus must not be erected in or under rooms occupied or

frequented (passages, covered courts, &c.) by human beings. Generators

and holders must only be erected in apartments covered with light roofs,

and separated from occupied rooms, barns, and stables by a fire-proof

wall, or by a distance of 15 feet. Any wall is to be considered fire-

proof which is built of solid brick, without openings, and one side of

which is "quite free." Apparatus may be erected in barns and stables,

provided the space required is partitioned off from the remainder by a

fire-proof wall.

2. The doors of apparatus sheds must open outwards, and must not

communicate directly with rooms where fires and artificial lights are

used.

3. Apparatus for the illumination of showmen's booths, "merry-go-rounds,"

shooting galleries, and the like must be erected outside the tents, and

be inaccessible to the public.

4. Permanent apparatus erected in the open air must be at least 15 feet

from an occupied building.

5. Apparatus sheds must be fitted at their highest points with outlet

ventilators of sufficient size; the ventilators leading straight through

the roof into the open air. They must be so arranged that the escaping

gases and vapours cannot enter rooms or chimneys.

6. The contacts of any electrical warning devices must be outside the

apparatus shed.

7. Acetylene plants must be prevented from freezing by erection in frost-

free rooms, or by the employment of a heating apparatus or other suitable

appliance. The heat must only be that of warm water or steam. Furnaces

for the heating appliance must be outside the rooms containing

generators, their subsidiary apparatus, or holders; and must be separated

from such rooms by fire-proof walls.

8. In one of the walls of the apparatus shed--if possible not that having

a door--a window must be fitted which cannot be opened; and outside that

window an artificial light is to be placed. In the usual way acetylene

lighting may be employed; but a lamp burning paraffin or oil, or a

lantern enclosing a candle, must always be kept ready for use in

emergencies. In all circumstances internal lighting is forbidden.

9. Every acetylene installation must be provided with a main cock, placed

in a conveniently accessible position so that the whole of the service

may be cut off from the plant.

10. The seller of an apparatus must provide his customer with a sectional

drawing, a description of the apparatus, and a set of rules for attending

to it. These are to be supplied in duplicate, and one set is to be kept

hanging up in the apparatus shed.

III. Rules for Working the Apparatus.

1. The apparatus must only be opened by daylight for addition of water.

If the generator is one of those in which the entire charge of carbide is

not gasified at once, addition of fresh carbide must only be made by

daylight.

2. All work required by the plant, or by any portion of it, and all

ordinary attendance needed must be performed by daylight.

3. All water-seals must be carefully kept full.

4. When any part of an acetylene apparatus or a gas-meter freezes,

notwithstanding the precautions specified in II., 7, it must be thawed

only by pouring hot water into or over it; flames, burning fuel, or red-

hot iron bars must not be used.

5. Alterations to any part of an apparatus which involve the operations

of soldering or riveting, &c., _i.e._, in which a fire must be used,

or a spark may be produced by the impact of hammer on metal, must only be

carried out by daylight in the open air after the apparatus has been

taken to pieces. First of all the plant must be freed from gas. This is

to be done by filling every part with water till the liquid overflows,

leaving the water in it for at least five minutes before emptying it

again.

6. The apparatus house must not be used for any other operation, nor

employed for the storage of combustible articles. It must be efficiently

ventilated, and always kept closed. A notice must be put upon the door

that unauthorised persons are not permitted to enter.

7. It in forbidden to enter the house with a burning lantern or lamp, to

strike matches, or to smoke therein.

8. A search for leaks in the pipes must not be made with the aid of a

light.

9. Alterations to the service must not be made while the pipes are under

pressure, but only after the main cock has been shut.

10. If portable apparatus, such as described in I., 12, are connected to

the burners with rubber tube, the tube must be fortified with an internal

or external spiral of wire. The tube must be fastened at both ends to the

cocks with thread, copper wire, or with ring clamps.

11. The preparation, storage, and use of compressed or liquefied

acetylene is forbidden. By compressed acetylene, however, is only to be

understood gas compressed to a pressure exceeding one effective

atmosphere. Acetylene compressed into porous matter, with or without

acetone, is excepted from this prohibition.

12. In the case of plants serving 50 lights or less, not more than 100

kilos. of carbide in closed vessels may be kept in the apparatus house

besides the drum actually in use.

A fresh drum is not to be opened before the previous one has been two-

thirds emptied. Opened drums must be closed with an iron watertight lid

covering the entire top of the vessel.

In the case of apparatus supplying over 500 lights, only one day's

consumption of carbide must be kept in the generator house. In other

respects the store of carbide for such installations is to be treated as

a regular carbide store.

13. Carbide drums must not be opened with the aid of a flame or a red-hot

iron instrument.

14. Acetylene apparatus must only be attended to by trustworthy and

responsible persons.

The rules issued by the AUSTRIAN GOVERNMENT in 1905 for the installation

of acetylene plant and the use of acetylene are divided into general

enactments relating to acetylene, and into special enactments in regard

to the apparatus and installation. The general enactments state that:

1. The preparation and use of liquid acetylene is forbidden.

2. Gaseous acetylene, alone, in admixture, or in solution, must not be

compressed above 2 atmospheres absolute except under special permission.

3. The storage of mixtures of acetylene with air or other gases

containing or evolving free oxygen is forbidden.

4. A description of every private plant about to be installed must be

submitted to the local authorities, who, according to its size and

character, may give permission for it to be installed and brought into

use either forthwith or after special inspection. Important alterations

to existing plant must be similarly notified.

5. The firms and fitters undertaking the installation of acetylene plant

must be licensed.

The special enactments fall under four headings, viz., (_a_)

apparatus; (_b_) plant houses; (_c_) pipes; (_d_)

residues.

In regard to apparatus it is enacted that:

1. The type of apparatus to be employed must be one which has been

approved by one of certain public authorities in the country.

2. A drawing and description of the construction of the apparatus and a

short explanation of the method of working it must be fixed in a

conspicuous position under cover in the apparatus house. The notice must

also contain approved general information as to the properties of calcium

carbide and acetylene, precautions that must be observed to guard against

possible danger, and a statement of how often the purifier will require

to be recharged.

3. The apparatus must be marked with the name of the maker, the year of

its construction, the available capacity of the gasholder, and the

maximum generating capacity per hour.

4. Each constituent of the plant must be proportioned to the maximum

hourly output of gas and in particular the available capacity of the

holder must be 75 per cent. of the latter. The apparatus must not be

driven above its nominal productive capacity.

5. The productive capacity of generators in which the gasholder has to be

opened or the bell removed before recharging, or for the removal of

sludge, must not exceed 50 litres per hour, nor may the charge of carbide

exceed 1 kilo.

6. Generators exceeding 50 litres per hour productive capacity must be

arranged so that they can be freed from air before use.

7. Generators exceeding 1500 litres per hour capacity must be arranged so

that the acetylene, contained in the parts of the apparatus which have to

be opened for recharging or for the removal of sludge, can be removed

before they are opened.

8. Automatic generators of which the decomposing chambers are built

inside the gasholder must not exceed 300 litres per hour productive

capacity.

9. Generators must be arranged so that after-generation cannot produce

objectionable results.

10. The holder of carbide-to-water generators must be large enough to

take all the gas which may be produced by the introduction of one charge

of carbide without undue pressure ensuing.

11. The maximum pressure permissible in any part of the apparatus is 1.1

atmosphere absolute.

12. The temperature in the gas space of a generator must never exceed 80°

13. Generating apparatus, &c., must be constructed in a workmanlike

manner of metal capable of resisting rust and distortion, and, where the

metal comes in contact with carbide or acetylene, it must not be one

(copper in particular) which forms an explosive compound with the gas.

Cocks and screw connexions, &c., of brass, bronze, &c., must always be

kept clean. Joints exposed to acetylene under pressure must be made by

riveting or welding except that in apparatus not exceeding 100 litres per

hour productive capacity double bending may be used.

14. Every apparatus must be fitted with a safety-valve or vent-pipe

terminating in a safe place in the open, and of adequate size.

15. Every apparatus must be provided with an efficient purifier so fitted

that it may be isolated from the rest of the plant and with due

consideration of the possible action of the purifying material upon the

metal used.

16. Mercury pressure gauges are prohibited. Liquid gauges, if used must

be double the length normally needed, and with a cock which in automatic

apparatus must be kept shut while it is in action.

17. Proper steps must always be taken to prevent the apparatus freezing.

In the absence of other precautions water-seals and pressure-gauges must

be filled with liquid having a sufficiently low freezing-point and

without action on acetylene or the containing vessel.

18. Signal devices to show the position of the gasholder bell must not be

capable of producing sparks inside the apparatus house.

19. Leaks must not be sought for with an open flame and repairs requiring

the use of a blow-pipe, &c., must only be carried out after the apparatus

has been taken to pieces or freed from gas by flooding.

20. Apparatus must only be attended to by trustworthy and responsible

adults.

21. Portable apparatus holding not more than 1 kilo. of carbide and of

not more than 50 litres per hour productive capacity, and apparatus fixed

and used out of doors are exempt from the foregoing regulations except

Nos. 11 and 12, and the first part of 13.

In regard to (_b_), plant houses, it is enacted that:

1. Rooms containing acetylene apparatus must be of ample size, used for

no other purpose, have water-tight floors, be warmed without fireplaces

or chimneys, be lighted from outside through an air-tight window by an

independent artificial light, have doors opening outwards, efficient

ventilation and a store of sand or like material for fire extinction.

Strangers must be warned away.

2. Apparatus of not more than 300 litres per hour productive capacity may

be erected in basements or annexes of dwelling houses, but if of over 50

litres per hour capacity must not be placed under rooms regularly

frequented. Rooms regularly frequented and those under the same must not

be used.

3. Apparatus of more than 300 litres per hour productive capacity must be

erected in an independent building at least 15 feet distant from other

property, which building, unless it is at least 30 feet distant, must be

of fire-proof material externally.

4. Gasholders exceeding 280 cubic foot in capacity must be in a detached

room or in the open and inaccessible to strangers, and at least 30 feet

from other property and with lightning conductors.

5. In case of fire the main cock must not be shut until it is ascertained

that no one remains in the room served with the gas.

6. All acetylene installations must be known to the local fire brigade.

In regard to (_c_), pipes, it is enacted that:

1. Mains for acetylene must be separated from the generating apparatus by

a cock, and under a five-minute test for pressure must not show a fall of

over eight-tenths inch when the pressure is 13.8 inches, or three times

the working pressure, whichever is greater.

2. The pipes must as a rule be of iron, though lead may be used where

they are uncovered and not exposed to risk of injury. Rubber connexions

may only be used for portable apparatus, and attached to a terminal on

the metal pipes provided with a cock, and be fastened at both ends so

that they will not slip off the nozzles.

In regard to (_d_), residues, it is enacted that special open or

well-ventilated pits must be provided for their reception when the

apparatus exceeds 300 litres per hour productive capacity. With smaller

apparatus they may be discharged into cesspools if sufficiently diluted.

The ITALIAN GOVERNMENT regulations in regard to acetylene plant are

divided into eight sections. The first of these relates to the production

and use of liquid and compressed acetylene. The production and use of

liquid acetylene is prohibited except under the provisions of the laws

relating to explosives. Neat acetylene must not be compressed to more

than l-1/2 atmospheres except that an absolute pressure of 10 atmospheres

is allowed when the gas is dissolved in acetone or otherwise rendered

free from risk. Mixtures of acetylene with air or oxygen are forbidden,

irrespective of the pressure or proportions. Mixtures of acetylene with

hydrocarbons, carbonic oxide, hydrogen and inert gases are permitted

provided the proportion of acetylene does not exceed 50 per cent. nor the

absolute pressure 10 atmospheres.

The second section relates to acetylene installations, which are

classified in four groups, viz., (_a_) fixed or portable apparatus

supplying not more than thirty burners consuming 20 litres per hour;

(_b_) private installations supplying between 30 and 200 such

burners; (_c_) public or works installations supplying between 30

and 200 such burners; (_d_) installations supplying more than 200

such burners.

The installations must comply with the following general conditions:

1. No part of the generator when working at its utmost capacity should

attain a temperature of more than 100° C.

2. The carbide must be completely decomposed in the apparatus so that no

acetylene can be evolved from the residue. The residues must be diluted

with water before being discharged into drains or cesspools, and sludge

storage-pits must be in the open.

3. The apparatus must preclude the escape of lime into the gas and water

connexions.

4. Glass parts must be adequately protected.

5. Rubber connexions between the generator, gasholder, and main are

absolutely prohibited with installations supplying more than 30 burners.

6. Cocks must be provided for cutting off the main and connexions from

the generator and gasholder.

7. Each burner must have an independent tap.

8. Generators of groups (_b_), (_c_), and (_d_) must be

constructed so that no after-generation of acetylene can take place

automatically and that any surplus gas would in any case be carried out

of the generator house by a vent-pipe.

The third section deals with generator houses, which must be well

ventilated and light; must not be used for any other purpose except to

store one day's consumption of carbide, not exceeding 300 kilos.; must be

fire-proof; must have doors opening outwards; and the vent-pipes must

terminate at a safe place in the open. Apparatus of group (_b_) must

not be placed in a dwelling-room and only in an adjoining room if the

gasholder is of less than 600 litres capacity. Apparatus of group

(_c_) must be in an independent building which must be at least 33

feet from occupied premises if the capacity of the gasholder is 6000

litres and upwards. Half this distance suffices for gasholders containing

600 to 6000 litres. These distances may be reduced at the discretion of

the local authorities provided a substantial partition wall at least 1

foot thick is erected. Apparatus of group (_d_) must be at least 50

feet from occupied premises and the gasholder and generator must not be

in the same building.

The fourth section deals with the question of authorisation for the

installation of acetylene plant. Apparatus of group (_a_) may be

installed without obtaining permission from any authorities. In regard to

apparatus of the other groups, permission for installation must be

obtained from local or other authorities.

The fifth section relates to the working of acetylene plant. It makes the

concessionaires and owners of the plant responsible for the manipulation

and supervision of the apparatus, and for the employment of suitable

operators, who must not be less than 18 years of age.

The sixth section relates to the inspection of acetylene plant from time

to time by inspectors appointed by the local or other authorities.

Apparatus of group (_a_) is not subject to these periodical

inspections.

The seventh section details the fees payable for the inspection of

installations and carbide stores, and fixes the penalties for non-

compliance with the regulations.

The eighth section refers to the notification of the position and

description of all carbide works, stores, and acetylene installations to

the local authorities.

The HUNGARIAN GOVERNMENT rules for the construction and examination of

acetylene plant forbid the use of copper and of its alloys; cocks,

however, may be made of a copper alloy. The temperature in the gas space

of a fixed generator must not exceed 50° C., in that of a portable

apparatus 80° C. The maximum effective pressure permissible is 0.15

atmosphere.

The CONSEIL D'HYGIÈNE DE LA SEINE IN FRANCE allows a maximum pressure of

1.5 metres, i.e., 59 inches, of water column in generators used for the

ordinary purposes of illumination; but apparatus intended to supply gas

to the low-pressure oxy-acetylene blowpipe (see Chapter IX.) may develop

up to 2.5 metres, or 98.5 inches of water pressure, provided copper and

its alloys are entirely excluded from the plant and from the delivery-

pipes.

The NATIONAL BOARD OF FIRE UNDERWRITERS OF THE UNITED STATES OF AMERICA

has issued a set of rules and requirements, of which those relating to

acetylene generators and plant are reproduced below. The underwriters

state that, "To secure the largest measure of safety to life and

property, these rules for the installation of acetylene gas machines must

be observed."

RULES FOR THE INSTALLATION AND USE OF ACETYLENE GAS GENERATORS.

[Footnote: The "gallon" of these rules is, of course, the American

gallon, which is equal to 0.83 English standard gallon.]

The use of liquid acetylene or gas generated therefrom is absolutely

prohibited.

Failure to observe these rules is as liable to endanger life as property.

To secure the largest measure of safety to life and property, the

following rules for the installation of acetylene gas machines must be

observed.

_Class A.--Stationary Automatic Apparatus._

1. FOUNDATIONS.--(_a_) Must, where practicable, be of brick, stone,

concrete or iron. If necessarily of wood they shall be extra heavy,

located in a dry place and open to the circulation of air.

The ordinary board platform is not satisfactory. Wooden foundations shall

be of heavy planking, joists or timbers, arranged so that the air will

circulate around them so as to form a firm base.

(_b_) Must be so arranged that the machine will be level and unequal

strain will not be placed on the generator or connexions.

2. LOCATION.--(_a_) Generators, especially in closely built up

districts should preferably be placed outside of insured buildings in

generator houses constructed and located in compliance with Rule 9.

(_b_) Generators must be so placed that the operating mechanism will

have room for free and full play and can be adjusted without artificial

light. They must not be subject to interference by children or careless

persons, and if for this purpose further enclosure is necessary, it must

be furnished by means of slatted partitions permitting the free

circulation of air.

(_c_) Generators which from their construction are rendered

inoperative during the process of recharging must be so located that they

can be recharged without the aid of artificial light.

(_d_) Generators must be placed where water will not freeze.

3. ESCAPES OR RELIEF-PIPES.--Each generator must be provided with an

escape or relief-pipe of ample size; no such pipe to be less than 3/4-

inch internal diameter. This pipe shall be substantially installed,

without traps, and so that any condensation will drain back to the

generator. It must be carried to a suitable point outside the building,

and terminate in an approved hood located at least 12 feet above ground

and remote from windows.

The hood must be constructed in such a manner that it cannot be

obstructed by rain, snow, ice, insects or birds.

4. CAPACITY.--(_a_) Must be sufficient to furnish gas continuously

for the maximum lighting period to all lights installed. A lighting

period of at least 5 hours shall be provided for in every case.

(_b_) Generators for conditions of service requiring lighting period

of more than 5 hours must be of sufficient capacity to avoid recharging

at night. The following ratings will usually be found advisable.

(i) For dwellings, and where machines are always used intermittently, the

generator must have a rated capacity equal to the total number of burners

installed.

(ii) For stores, opera houses, theatres, day-run factories, and similar

service, the generator must have a rated capacity of from 30 to 50 per

cent, in excess of the total number of burners installed.

(iii) For saloons and all night or continued service, the generator must

have a rated capacity of from 100 to 200 per cent. in excess of the total

number of burners installed.

(_c_) A small generator must never be installed to supply a large

number of lights, even though it seems probable that only a few lights

will be used at a time. _An overworked generator adds to the cost of

producing acetylene gas_.

5. CARBIDE CHARGES.--Must be sufficient to furnish gas continuously for

the maximum lighting period to all burners installed. In determining

charges lump carbide must be estimated as capable of producing 4-1/2

cubic foot of gas to the pound, commercial 1/4-inch carbide 4 cubic feet

of gas to the pound, and burners must be considered as requiring at least

25 per cent. more than their rated consumption of gas.

6. BURNERS.--Burners consuming one-half of a cubic foot of gas per hour

are considered standard in rating generators. Those having a greater or

less capacity will decrease or increase the number of burners allowable

in proportion.

Burners usually consume from 25 to 100 per cent. more than their rated

consumption of gas, depending largely on the working pressure. The so-

called 1/2-foot burner when operated at pressures of from 20- to 25-

tenths inches water column (2 to 2-1/2 inches) is usually used with best

economy.

7. PIPING.--(_a_) Connexions from generators to service-pipes must

be made with right and left thread nipples or long thread nipples with

lock nuts. All forms of unions are prohibited.

(_b_) Piping must, as far as possible, be arranged so that any

moisture will drain back to the generator. If low points occur of

necessity in any piping, they must be drained through tees into drip cups

permanently closed with screw caps or plugs. No pet-cocks shall be used.

(_c_) A valve and by-pass connexion must be provided from the

service-pipe to the blow-off for removing the gas from the holder in case

it should be necessary to do so.

(_d_) The schedule of pipe sizes for piping from generators to

burners should conform to that commonly used for ordinary gas, but in no

case must the feeders be smaller than three-eighths inch.

The following schedule is advocated:

3/8 inch pipe, 26 feet, three burners.

1/2 inch pipe, 30 feet, six burners.

3/4 inch pipe, 50 feet, twenty burners.

1 inch pipe, 70 feet, thirty-five burners.

1-1/4 inch pipe, 100 feet, sixty burners.

1-1/2 inch pipe, 150 feet, one hundred burners.

2 inch pipe, 200 feet, two hundred burners.

2-1/2 inch pipe, 300 feet, three hundred burners.

3 inch pipe, 450 feet, four hundred and fifty burners,

3-1/2 inch pipe, 500 feet, six hundred burners.

4 inch pipe, 600 feet, seven hundred and fifty burners.

(_e_) Machines of the carbide-feed type must not be fitted with

continuous drain connexions leading to sewers, but must discharge into

suitable open receptacles which may have such connections.

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 16 / 22 章

USE OF OIL IN GENERATORS.--Calcium carbide is a material which is only