Fermentation:--_A Dictionary of Arts, Manufactures and Mines containing a clear exposition of their principles and practice

March 24. pitched the tun at 51°: yeast 4 gallons.

Temp. Gravity.

25. 52° 41 pounds.

28. 56° 39

30. 60° 34

April 1. 62° 32

4. 65° 29 added 1 lb. of yeast.

5. 66° 25

6. 67° 23

7. 67° 20

8. 66° 18

9. 66° 15

10. 64° 14·5 cleansed[7].

[7] BREWING (Society for diffusing Useful Knowledge), p. 156.

The following table shows the origin and the result of fermentation, in

a number of practical experiments:--

+--------+----------+-----------+----------+------------+

+--------+----------+-----------+----------+------------+

| 1·0950 | 88·75 | 1·0500 | 40·25 | 0·478 |

| 1·0918 | 85·62 | 1·0420 | 38·42 | 0·552 |

| 1·0829 | 78·125 | 1·0205 | 16·87 | 0·787 |

| 1·0862 | 80·625 | 1·0236 | 20·00 | 0·757 |

| 1·0780 | 73·75 | 1·0280 | 24·25 | 0·698 |

| 1·0700 | 65·00 | 1·0285 | 25·00 | 0·615 |

| 1·1002 | 93·75 | 1·0400 | 36·25 | 0·613 |

| 1·1025 | 95·93 | 1·0420 | 38·42 | 0·600 |

| 1·0978 | 91·56 | 1·0307 | 27·00 | 0·705 |

| 1·0956 | 89·37 | 1·0358 | 32·19 | 0·640 |

| 1·1130 | 105·82 | 1·0352 | 31·87 | 0·661 |

| 1·1092 | 102·187 | 1·0302 | 26·75 | 0·605 |

| 1·1171 | 110·00 | 1·0400 | 36·25 | 0·669 |

| 1·1030 | 96·40 | 1·0271 | 23·42 | 0·757 |

| 1·0660 | 61·25 | 1·0214 | 17·80 | 0·709 |

+--------+----------+-----------+----------+------------+

The second column here does not represent, I believe, the solid extract,

but the pasty extract obtained as the basis of Mr. Allen’s

saccharometer, and therefore each of its numbers is somewhat too high.

The last column, also, must be in some measure erroneous, on account of

the quantity of alcohol dissipated during the process of fermentation.

It must be likewise incorrect, because the density due to the saccharine

matter will be partly counteracted, by the effect of the alcohol present

in the fermented liquor. In fact, the attenuation does not correspond to

the strength of the wort; being greatest in the third brewing, and

smallest in the first. The quantity of yeast for the above ale brewings

in the table was, upon an average, one gallon for 108 gallons; but it

varied with its quality, and with the state of the weather, which, when

warm, permits much less to be used with propriety.

The good quality of the malt, and the right management of the mashing,

may be tested by the quantity of saccharine matter contained in the

successively drawn worts. With this view, an aliquot portion of each of

them should be evaporated by a safety-bath heat to a nearly concrete

consistence, and then mixed with twice its volume of strong spirit of

wine. The truly saccharine substance will be dissolved, while the starch

and other matters will be separated; after which the proportions of each

may be determined by filtration and evaporation. Or an equally correct,

and much more expeditious, method of arriving at the same result would

be, after agitating the viscid extract with the alcohol in a tall glass

cylinder, to allow the insoluble fecula to subside, and then to

determine the specific gravity of the supernatant liquid by a

hydrometer. The additional density which the alcohol has acquired will

indicate the quantity of malt sugar which it has received. The following

table, constructed by me, at the request of Henry Warburton, Esq., M.

P., chairman of the Molasses Committee of the House of Commons in 1830,

will show the brewer the principle of this important inquiry. It

exhibits the quantity in grains weight of sugar requisite to raise the

specific gravity of a gallon of spirit of different densities to the

gravity of water = 1·000.

Specific Gravity of Grains, Weight of Sugar in the

Spirit. Gallon Imperial.

0·995 0·980

0·990 1·890

0·985 2·800

0·980 3·710

0·975 4·690

0·970 5·600

0·965 6·650

0·960 7·070

0·955 8·400

0·950 9·310

The immediate purpose of this table was to show the effect of saccharine

matter in disguising the presence or amount of alcohol in the weak

feints of the distiller. But a similar table might easily be

constructed, in which, taking a uniform quantity of alcohol of 0·825,

for example, the quantity of sugar in any wort-extract would be shown by

the increase of specific gravity which the alcohol received from

agitation with a certain weight of the wort, inspissated to a nearly

solid consistence by a safety-pan, made on the principle of my patent

sugar-pan. (See SUGAR.) Thus, the normal quantities being 1000 grain

measures of alcohol, and 100 grains by weight of inspissated

mash-extract, the hydrometer would at once indicate, by help of the

table, first, the quantity per cent. of truly saccharine matter, and

next, by subtraction, that of farinaceous matter present in it.

[Illustration: 103]

_Plan, Machinery, and Utensils of a great Brewery._--_Figs._ 103. and

104. represent the arrangement of the utensils and machinery in a porter

brewery on the largest scale; in which, however, it must be observed

that the elevation _fig._ 103. is in a great degree imaginary as to the

plane upon which it is taken; but the different vessels are arranged so

as to explain their uses most readily, and at the same time to

preserve, as nearly as possible, the relative positions which are

usually assigned to each in works of this nature.

The malt for the supply of the brewery is stored in vast granaries or

malt-lofts, usually situated in the upper part of the buildings. Of

these, I have been able to represent only one, at A, _fig._ 103.: the

others, which are supposed to be on each side of it, cannot be seen in

this view. Immediately beneath the granary A, on the ground floor, is

the mill; in the upper story above it, are two pairs of rollers, _fig._

101, 102, and 103, under _a_, _a_, for bruising or crushing the grains

of the malt. In the floor beneath the rollers are the mill-stones _b_,

_b_, where the malt is sometimes ground, instead of being merely bruised

by passing between the rollers, under _a_, _a_.

The malt, when prepared, is conveyed by a trough into a chest _d_, to

the right of _b_, from which it can be elevated by the action of a

spiral screw, _fig._ 105., enclosed in the sloping tube _e_, into the

large chest or binn B, for holding ground malt, situated immediately

over the mash-tun D. The malt is reserved in this binn till wanted, and

it is then let down into the mashing-tun, where the extract is obtained

by hot water supplied from the copper G, seen to the right of B.

The water for the service of the brewery is obtained from the well E,

seen beneath the mill to the left, by a lifting pump worked by the steam

engine; and the forcing-pipe _f_ of this pump conveys the water up to

the large reservoir or water-back F, placed at the top of the

engine-house. From this cistern, iron pipes are laid to the copper G (on

the right-hand side of the figure), as also to every part of the

establishment where cold water can be wanted for cleaning and washing

the vessels. The copper G can be filled with cold water by merely

turning a cock; and the water, when boiled therein, is conveyed by the

pipe _g_ into the bottom of the mash-tun D. It is introduced beneath a

false bottom, upon which the malt lies, and, rising up through the holes

in the false bottom, it extracts the saccharine matter from the malt; a

greater or less time being allowed for the infusion, according to

circumstances. The instant the water is drawn off from the copper, fresh

water must be let into it, in order to be ready for boiling the second

mashing; because the copper must not be left empty for a moment,

otherwise the intense heat of the fire would destroy its bottom. For the

convenience of thus letting down at once as much liquor as will fill the

lower part of the copper, a pan or second boiler is placed over the top

of the copper, as seen in _fig._ 103.; and the steam rising from the

copper communicates a considerable degree of heat to the contents of the

pan, without any expense of fuel. This will be more minutely explained

hereafter. (_See fig._ 107.)

During the process of mashing, the malt is agitated in the mash-tun, so

as to expose every part to the action of the water. This is done by a

mechanism contained within the mash-tun, which is put in motion by a

horizontal shaft above it, H, leading from the mill. The mash machine is

shown separately in _fig._ 106. When the operation of mashing is

finished, the wort or extract is drained down from the malt into the

vessel I, called the _under-back_, immediately below the mash-tun, of

like dimensions, and situated always on a lower level, for which reason

it has received this name. Here the wort does not remain longer than is

necessary to drain off the whole of it from the tun above. It is then

pumped up by the three-barrelled pump _k_, into the pan upon the top of

the copper, by a pipe which cannot be seen in this section. The wort

remains in the pan until the water for the succeeding mashes is

discharged from the copper. But this delay is no loss of time, because

the heat of the copper, and the steam arising from it, prepare the wort,

which had become cooler, for boiling. The instant the copper is emptied,

the first wort is let down from the pan into the copper, and the second

wort is pumped up from the under-back into the upper pan. The proper

proportion of hops is thrown into the copper through the near hole, and

then the door is shut down, and screwed fast, to keep in the steam, and

cause it to rise up through pipes into the pan. It is thus forced to

blow up through the wort in the pan, and communicates so much heat to

it, or water, called _liquor_ by the brewers, that either is brought

near to the boiling point. The different worts succeed each other

through all the different vessels with the greatest regularity, so that

there is no loss of time, but every part of the apparatus is constantly

employed. When the ebullition has continued a sufficient period to

coagulate the grosser part of the extract, and to evaporate part of the

water, the contents of the copper are run off through a large cock into

the _jack-back_ K, below G, which is a vessel of sufficient dimensions

to contain it, and provided with a bottom of cast-iron plates,

perforated with small holes, through which the wort drains and leaves

the hops. The hot wort is drawn off from the jack-back through the pipe

_h_ by the three-barrelled pump, which throws it up to the coolers L, L,

L; this pump being made with different pipes and cocks of communication,

to serve all the purposes of the brewery except that of raising the cold

water from the well. The coolers L, L, L, are very shallow vessels,

built over one another in several stages: and that part of the building

in which they are contained is built with lattice-work or or shutter

flaps, on all sides, to admit free currents of air. When the wort is

sufficiently cooled to be put to the first fermentation, it is conducted

in pipes from all the different coolers to the large fermenting vessel

or gyle-tun M, which, with another similar vessel behind it, is of

sufficient capacity to contain all the beer of one day’s brewings.

Whenever the first fermentation is concluded, the beer is drawn off from

the great fermenting vessel M, into the small fermenting casks or

cleansing vessels N, of which there are a great number in the brewery.

They are placed four together, and to each four a common spout is

provided to carry off the yeast, and conduct it into the troughs _n_,

placed beneath. In these cleansing vessels the beer remains till the

fermentation is completed; and it is then put into the store-vats, which

are casks or tuns of an immense size, where it is kept till wanted, and

is finally drawn off into barrels, and sent away from the brewery. The

store-vats are not represented in the figure: they are of a conical

shape, and of different dimensions, from fifteen to twenty feet

diameter, and usually from fifteen to twenty feet in depth. The

steam-engine which puts all the machine in motion is exhibited in its

place, on the left side of the figure. On the axis of the large

fly-wheel is a bevelled spur-wheel, which turns another similar wheel

upon the end of a horizontal shaft, which extends from the engine-house

to the great horse-wheel, set in motion by means of a spur-wheel. The

horse-wheel drives all the pinions for the mill-stones _b_, _b_, and

also the horizontal axis which works the three-barrelled pump _k_. The

rollers _a_, _a_, are turned by a bevel wheel upon the upper end of the

axis of the horse-wheel, which is prolonged for that purpose; and the

horizontal shaft H, for the mashing engine, is driven by a pair of bevel

wheels. There is likewise a sack-tackle, which is not represented. It is

a machine for drawing up the sacks of malt from the court-yard to the

highest part of the building, whence the sacks are wheeled on a truck to

the malt-loft A, and the contents of the sacks are discharged.

The horse-wheel is intended to be driven by horses occasionally, if the

steam-engine should fail; but these engines are now brought to such

perfection that it is very seldom any recourse of this kind is needed.

[Illustration: 104]

_Fig._ 104. is a representation of the _fermenting house_ at the brewery

of Messrs. Whitbread and Company, Chiswell Street, London, which is one

of the most complete in its arrangement in the world: it was erected

after the plan of Mr. Richardson, who conducts the brewing at those

works. The whole of _fig._ 104. is to be considered as devoted to the

same object as the large vessel M and the casks N, _fig._ 103. In _fig._

104., _r r_ is the pipe which leads from the different coolers to convey

the wort to the great fermenting vessels or squares M, of which there

are two, one behind the other; _f f_ represents a part of the great pipe

which conveys all the water from the well E, _fig._ 103, up to the water

cistern F. This pipe is conducted purposely up the wall of the

fermenting-house, _fig._ 104, and has a cock in it, near _r_, to stop

the passage. Just beneath this passage a branch-pipe _p_ proceeds, and

enters a large pipe _x x_, which has the former pipe _r_ withinside of

it. From the end of the pipe _x_, nearest to the squares M, another

branch _n n_ proceeds, and returns to the original pipe _f_, with a cock

to regulate it. The object of this arrangement is to make all, or any

part, of the cold water flow through the pipe _x x_, which surrounds the

pipe _r_, formed only of thin copper, and thus cool the wort passing

through the pipe _r_, until it is found by the thermometer to have the

exact temperature which is desirable before it is put to ferment in the

great square M. By means of the cocks at _n_ and _p_, the quantity of

cold water passing over the surface of the pipe _r_ can be regulated at

pleasure, whereby the heat of the wort, when it enters into the square,

may be adjusted within half a degree.

When the first fermentation in the squares M M is finished, the beer is

drawn off from them by pipes marked _c_, and conducted by its branches W

W W, to the different rows of fermenting-tuns, marked N N, which occupy

the greater part of the building. In the hollow between every two rows

are placed large troughs, to contain the yeast which they throw off. The

figure shows that the small tuns are all placed on a lower level than

the bottom of the great vessels M, so that the beer will flow into them,

and, by hydrostatic equilibrium, will fill them to the same level. When

they are filled, the communication-cock is shut; but, as the working off

the yeast diminishes the quantity of beer in each vessel, it is

necessary to replenish them from time to time. For this purpose, the two

large vats O O are filled from the great squares M M, before any beer is

drawn off into the small casks N, and this quantity of beer is reserved

at the higher level for filling up. The two vessels O O are, in reality,

situated between the two squares M M; but I have been obliged to place

them thus in the section, in order that they may be seen. Near each

filling-up tun O is a small cistern _t_ communicating with the tun O by

a pipe, which is closed by a float-valve. The small cisterns _t_ are

always in communication with the pipes which lead to the small

fermenting vessels N; and therefore the surface of the beer in all the

tuns, and in the cisterns, will always be at the same level; and as this

level subsides by the working off of the yeast from the tuns, the float

sinks and opens the valve, so as to admit a sufficiency of beer from the

filling-up tuns O, to restore the surfaces of the beer in all the tuns,

and also in the cistern _t_, to the original level. In order to carry

off the yeast which is produced by the fermentation of the beer in the

tuns O O, a conical iron dish or funnel is made to float upon the

surface of the beer which they contain; and from the centre of this

funnel a pipe, _o_, descends, and passes through the bottom of the tun,

being packed with a collar of leather, so as to be water-tight; at the

same time that it is at liberty to slide down, as the surface of the

beer descends in the tun. The yeast flows over the edge of this

funnel-shaped dish, and is conveyed down the pipe to a trough beneath.

Beneath the fermenting-house are large arched vaults, P, built with

stone, and lined with stucco. Into these the beer is let down in casks

when sufficiently fermented, and is kept in store till wanted. These

vaults are used at Mr. Whitbread’s brewery, instead of the great

store-vats of which we have before spoken, and are in some respects

preferable, because they preserve a great equality of temperature, being

beneath the surface of the earth.

The malt-rollers, or machines for bruising the grains of the malt,

_fig._ 101. 102., have been already described. The malt is shot down

from A, _fig._ 103., the malt-loft, into the hopper; and from this it is

let out gradually through a sluice or sliding shuttle, _a_, _fig._ 103.

and falls between the rollers.

[Illustration: 105]

_Fig._ 105. is the screw by which the ground or bruised malt is raised

up, or conveyed from one part of the brewery to another. K is an

inclined box or trough, in the centre of which the axis of the screw H

is placed; the spiral iron plate or worm, which is fixed projecting from

the axis, and which forms the screw, is made very nearly to fill the

inside of the box. By this means, when the screw is turned round by the

wheels E F, or by any other means, it raises up the malt from the box

_d_, and delivers it at the spout G.

This screw is equally applicable for conveying the malt horizontally in

the trough K, as slantingly; and similar machines are employed in

various parts of breweries for conveying the malt wherever the situation

of the works require.

[Illustration: 106]

_Fig._ 106. is the mashing-machine. _a a_ is the tun, made of wood

staves, hooped together. In the centre of it rises a perpendicular

shaft, _b_, which is turned slowly round by means of the bevelled wheels

_t u_ at the top. _c c_ are two arms, projecting from that axis, and

supporting the short vertical axis _d_ of the spur-wheel _x_, which is

turned by the spur-wheel _w_; so that, when the central axis _b_ is made

to revolve, it will carry the thick short axle _d_ round the tun in a

circle. That axle _d_ is furnished with a number of arms, _e e_, which

have blades placed obliquely to the plane of their motion. When the

axis is turned round, these arms agitate the malt in the tun, and give

it a constant tendency to rise upwards from the bottom.

The motion of the axle _d_ is produced by a wheel, _x_, on the upper end

of it, which is turned by a wheel, _w_, fastened on the middle of the

tube _b_, which turns freely round upon its central axis. Upon a higher

point of the same tube _b_ is a bevel wheel, _o_, receiving motion from

a bevel wheel, _q_, fixed upon the end of the horizontal axis _n n_,

which gives motion to the whole machine. This same axis has a pinion,

_p_, upon it, which gives motion to the wheel _r_, fixed near the middle

of a horizontal axle, which, at its left hand end, has a bevel pinion,

_t_, working the wheel _u_, before mentioned. By these means, the

rotation of the central axis _b_ will be very slow compared with the

motion of the axle _d_; for the latter will make seventeen or eighteen

revolutions on its own axis in the same space of time that it will be

carried once round the tun by the motion of the shaft _b_. At the

beginning of the operation of mashing, the machine is made to turn with

a slow motion; but, after having wetted all the malt by one revolution,

it is driven quicker. For this purpose, the ascending-shaft _f g_, which

gives motion to the machine, has two bevel wheels, _h i_, fixed upon a

tube, _f g_, which is fitted upon a central shaft. These wheels actuate

the wheels _m_ and _o_, upon the end of the horizontal shaft _n n_; but

the distance between the two wheels _h_ and _i_ is such, that they

cannot be engaged both at once with the wheels _m_ and _o_; but the tube

_f g_, to which they are fixed, is capable of sliding up and down on its

central axis sufficiently to bring either wheel _h_ or _i_ into geer

with its corresponding wheel _o_ or _m_, upon the horizontal shaft; and

as the diameters of _n o_, and _i m_, are of very different proportions,

the velocity of the motion of the machine can be varied at pleasure, by

using one or other. _k_ and _k_ are two levers, which are forked at

their extremities, and embrace collars at the ends of the tube _f g_.

These levers being united by a rod, _l_, the handle _k_ gives the means

of moving the tube _f g_, and its wheels _h i_, up or down, to throw

either the one or the other wheel into geer.

The object of boiling the wort is not merely evaporation and

concentration, but extraction, coagulation, and, finally, combination

with the hops; purposes which are better accomplished in a deep confined

copper, by a moderate heat, than in an open shallow pan with a quick

fire. The copper being encased above in brickwork, retains its digesting

temperature much longer than the pan could do. The waste steam of the

close kettle, moreover, can be economically employed in communicating

heat to water or weak worts; whereas the exhalations from an open pan

would prove a nuisance, and would need to be carried off by a hood. The

boiling has a four-fold effect: 1. it concentrates the wort; 2. during

the earlier stages of heating, it converts the starch into sugar,

dextrine, and gum, by means of the diastase; 3. it extracts the

substance of the hops diffused through the wort; 4. it coagulates the

albuminous matter present in the grain, or precipitates it by means of

the tannin of the hops.

The degree of evaporation is regulated by the nature of the wort, and

the quality of the beer. Strong ale and stout for keeping, require more

boiling than ordinary porter or table-beer brewed for immediate use. The

proportion of the water carried off by evaporation is usually from a

seventh to a sixth of the volume. The hops are introduced during the

progress of the ebullition. They serve to give the beer not only a

bitter aromatic taste, but also a keeping quality, or they counteract

its natural tendency to become sour; an effect partly due to the

precipitation of the albumen and starch, by their resinous and tanning

constituents, and partly to the antifermentable properties of their

lupuline, bitter principle, ethereous oil, and resin. In these respects,

there is none of the bitter plants which can be substituted for hops

with advantage. For strong beer, powerful fresh hops should be selected;

for weaker beer, an older and weaker article will suffice.

The hops are either boiled with the whole body of the wort, or extracted

with a portion of it; and this concentrated extract added to the rest.

The stronger the hops are, the longer time they require for extraction

of their virtues; for strong hops, an hour and a half or two hours

boiling may be proper; for a weaker sort, half an hour or an hour may be

sufficient; but it is never advisable to push this process too far, lest

a disagreeable bitterness, without aroma, be imparted to the beer. In

our breweries, it is the practice to boil the hops with a part of the

wort, and to filter the decoction through a drainer, called the _jack

hop-back_. The proportion of hops to malt is very various; but, in

general, from a pound and a quarter to a pound and a half of the former

are taken for 100 lbs. of the latter in making good table-beer. For

porter and strong ale, 2 pounds of hops are used, or even more; for

instance, one pound of hops to a bushel of malt, if the beer be destined

for the consumption of India.

During the boiling of the two ingredients, much coagulated albuminous

matter, in various states of combination, makes its appearance in the

liquid, constituting what is called the _breaking or curdling of the

wort_, when numerous minute flocks are seen floating in it. The

resinous, bitter, and oily-ethereous principles of the hops combine with

the sugar and gum, or dextrine of the wort; but for this effect they

require time and heat; showing that the boil is not a process of mere

evaporation, but one of chemical reaction. A yellowish-green pellicle of

hop-oil and resin appears upon the surface of the boiling wort, in a

somewhat frothy form: when this disappears, the boiling is presumed to

be completed, and the beer is strained off into the cooler. The

residuary hops may be pressed and used for an inferior quality of beer;

or they may be boiled with fresh wort, and be added to the next brewing

charge.

_Figs._ 107, 108. represent the copper of a London brewery. _Fig._ 107.

is a vertical section; _fig._ 108., a ground-plan of the fire-grate and

flue, upon a smaller scale: _a_ is the close copper kettle, having its

bottom convex within; _b_ is the open pan placed upon its top. From the

upper part of the copper, a wide tube, _c_, ascends, to carry off the

steam generated during the ebullition of the wort, which is conducted

through four downwards-slanting tubes, _d d_ (two only are visible in

this section), into the liquor of the pan _b_, in order to warm its

contents. A vertical iron shaft or spindle, _e_, passes down through the

tube _c_, nearly to the bottom of the copper, and is there mounted with

an iron arm, called _a rouser_, which carries round a chain hung in

loops, to prevent the hops from adhering to the bottom of the boiler.

Three bent stays, _f_, are stretched across the interior, to support the

shaft by a collet at their middle junction. The shaft carries at its

upper end a bevel wheel, _g_, working into a bevel pinion upon the axis

_h_, which may be turned either by power or by hand. The _rouser_ shaft

may be lifted by means of the chain _i_, which, going over two pulleys,

has its end passed round the wheel and axle _k_, and is turned by a

winch: _l_ is a tube for conveying the waste steam into the chimney _m_.

[Illustration: 107 108]

The heat is applied as follows:--For heating the colossal coppers of the

London breweries, two separate fires are required, which are separated

by a narrow wall of brickwork, _n_, _fig._ 107, 108. The dotted circle

_a´ a´_ indicates the largest circumference of the copper, and _b´ b´_

its bottom; _o o_ are the grates upon which the coals are thrown, not

through folding doors (as of old), but through a short slanting iron

hopper, shown at _p_, _fig._ 107., built in the wall, and kept

constantly filled with the fuel, in order to exclude the air. Thus the

lower stratum of coals gets ignited before it reaches the grate. Above

the hopper _p_, a narrow channel is provided for the admission of

atmospherical air, in such quantity merely as may be requisite to

complete the combustion of the smoke of the coals. Behind each grate

there is a fire-bridge, _r_, which reflects the flame upwards, and

causes it to play upon the bottom of the copper. The burnt air then

passes round the copper in a semicircular flue, _s s_, from which it

flows off into the chimney _m_, on whose under end a sliding

damper-plate, _t_, is placed, for tempering the draught. When cold air

is admitted at this orifice, the combustion of the fuel is immediately

checked. There is, besides, another slide-plate at the entrance of the

slanting flue into the vertical chimney, for regulating the play of the

flame under and around the copper. If the plate _t_ be opened, and the

other plate shut, the power of the fire is suspended, as it ought to be,

at the time of emptying the copper. Immediately over the grate is a

brick arch, _u_, to protect the front edge of the copper from the first

impulsion of the flame. The chimney is supported upon iron pillars, _v

v_; _w_ is a cavity closed with a slide-plate, through which the ashes

may be taken out from behind, by means of a long iron hook.

[Illustration: 109]

_Fig._ 109. represents one of the sluice-cocks, which are used to make

the communications of the pipes with the pumps, or other parts of the

brewery. B B represents the pipe in which the cock is placed. The two

parts of this pipe are screwed to the side of a box, C C, in which a

slider, A, rises and falls, and intercepts, at pleasure, the passage of

the pipe. The slider is moved by the rod _a_. This passes through a

stuffing-box, in the top of the box which contains the slider, and has

the rack _b_ fastened to it. The rack is moved by a pinion fixed upon

the axis of a handle _e_, and the rack and pinion are contained in a

frame _d_ which is supported by two pillars. The frame contains a small

roller behind the rack, which bears it up towards the pinion, and keeps

its teeth up to the teeth of the pinion. The slider A is made to fit

accurately against the internal surface of the box C, and to bear

against this surface by the pressure of a spring, so as to make a

perfectly close fitting.

[Illustration: 110]

_Fig._ 110. is a small cock to be placed in the side of the great store

vats, for the purpose of drawing off a small quantity of beer, to taste

and try its quality. A is a part of the stave or thickness of the great

store vat; into this the tube B of the cock is fitted, and is held tight

in its place by a nut, _a a_, screwed on withinside. At the other end of

the tube B, a plug, _c_, is fitted, by grinding it into a cone, and it

is kept in by a screw. This plug has a hole up the centre of it, and

from this a hole proceeds sidewise, and corresponds with a hole made

through the side of the tube when the cock is open; but when the plug

_c_ is turned round, the hole will not coincide, and then the cock will

be shut. D is the handle or key of the cock, by which its plug is turned

to open or shut it: this handle is put up the bore of the tube (the

cover E being first unscrewed and removed), and the end of it is adapted

to fit the end of the plug of the cock. The handle has a tube or passage

bored up it, to convey the beer away from the cock when it is opened,

and from this the passage _f_, through the handle, leads, to draw the

beer into a glass or tumbler. The hole in the side of the plug is so

arranged, that, when the handle is turned into a perpendicular

direction, with the passage _f_ downwards, the cock will be open. The

intention of this contrivance is, that there shall be no considerable

projection beyond the surface of the tun; because it sometimes happens

that a great hoop of the tun breaks, and, falling down, its great weight

would strike out any cock which had a projection; and, if this happened

in the night, much beer might be lost before it was discovered. The cock

above described, being almost wholly withinside, and having scarcely any

projection beyond the outside surface of the tun, is secure from this

accident.

[Illustration: 111]

_Fig._ 111. is a small contrivance of a vent peg, to be screwed into the

head of a common cask when the beer is to be drawn off from it, and it

is necessary to admit some air to allow the beer to flow. A A represents

a portion of the head of the cask into which the tube B is screwed. The

top of this tube is surrounded by a small cup, from which project the

two small handles C C, by which the peg is turned round to screw it into

the cask. The cup round the other part of the tube, is filled with

water; into this a small cup, D, is inverted; in consequence, the air

can gain admission into the cask when the pressure within is so far

diminished, that the air will bubble up through the water, and enter

beneath the small cup D.

The most efficient substance for fining beer hitherto discovered is

isinglass, which is prepared by solution in vinegar or old stale beer,

and this solution is afterwards reduced with thin mild beer generally

brewed for the purpose, in all large establishments, from a raw or

return wort. It must next be passed through a fine hair sieve, by means

of rubbing it down with a hard hair-brush, and brought to the proper

consistency by thin mild beer. If properly made, it will be clear,

transparent, and free from feculencies. Finings serve excellently to

remove any extraneous matter that may be found floating in the beer, and

thus changes it from bright to brilliant. The common quantity used is

from a pint to a quart per barrel, according to the nature of the beer.

To ascertain whether the beer is in a fit state for fining, put it into

a long glass cylindric vessel, and add to it a teaspoonful, or thereby,

of the fining; then give the mixture a good shake, by turning the vessel

up and down, after closing its mouth with the palm of the hand. If the

beer has been well brewed, its aptitude to become bright will be soon

shown by the mixture getting thick and curdy; a bright portion will

generally show itself at the bottom or middle; after which the finings

will gradually mount to the top, taking up all the impurities along with

them, till the whole becomes brilliant. Some have said that the finings

should carry the impurities down to the bottom; but this, according to

Mr. Black[8], takes place only with stubborn beer, which would not

become thoroughly bright with any quantity of finings which could be

introduced. Finings have usually a specific gravity of from 1·010 to

1·016, and, when added to beer in a fit condition for fining, invariably

go to the top, and not to the bottom. In fining beer in a barrel laid on

its side, if the finings do not make their appearance at the bung-hole,

the beer will not become bright. The isinglass must not be dissolved

with heat, nor in hot water.

[8] Treatise on Brewing, 8vo, p. 68.

Beer brewed from imperfectly malted grain, or from a mixture of malt and

raw corn, gives a fermentation quite different in flavour from that of

beer from sound malt. The nose is, in fact, the best guide to the

experienced brewer for ascertaining whether his process is going on well

or ill.

Ropiness is a morbid state of beer, which is best remedied, according to

Mr. Black, by putting the beer into a vat with a false bottom, and

adding, per barrel, 4 or 5 pounds of hops, taken gradually away after

the first boilings of the worts; and to them may be added about half a

pound per barrel of mustard-seed. Rouse the beer as the hops are

gradually introduced, and, in some months, the ropiness will be

perfectly cured. The beer should be drawn off from below the false

bottom.

For theoretical views, see FERMENTATION; and for wort-cooling apparatus,

see REFRIGERATOR.

BEET-ROOT SUGAR. See SUGAR.

BELL-METAL, an alloy of copper and tin. See COPPER.

BELLOWS. See METALLURGY.

BEN OIL. See OIL OF BEN.

BENGAL STRIPES. Ginghams; a kind of cotton cloth woven with coloured

stripes.

BENJAMIN or BENZOIN. (_Benjoin_, Fr.; _Benzöe_, Germ.) A species of

resin used chiefly in perfumery. It is extracted by incision from the

trunk and branches of the _styrax benzoin_, which grows in Java,

Sumatra, Santa Fé, and in the kingdom of Siam. The plant belongs to the

decandria monogynia of Linnæus, and the natural family of the ebenaceæ.

It hardens readily in the air, and comes to us in brittle masses, whose

fracture presents a mixture of red, brown, and white grains of various

sizes, which, when white, and of a certain shape, have been called

_amygdaloid_, from their resemblance to almonds. The _sorted_ benzoin

is, on the other hand, very impure.

The fracture of benzoin is conchoidal, and its lustre greasy: its

specific gravity varies from 1·063 to 1·092. It has an agreeable smell,

somewhat like vanilla, which is most manifest when it is ground. It

enters into fusion at a gentle heat, and then exhales a white smoke,

which may be condensed into the acicular crystals of benzoic acid, of

which it contains 18 parts in the hundred. Stoltze recommends the

following process for extracting the acid. The resin is to be dissolved

in 3 parts of alcohol, the solution is to be introduced into a retort,

and a solution of carbonate of soda dissolved in dilute alcohol is to be

gradually added to it, till the free acid be neutralised; and then a

bulk of water equal to double the weight of the benzoin is to be poured

in. The alcohol being drawn off by distillation, the remaining liquor

contains the acid, and the resin floating upon it may be skimmed off and

washed, when its weight will be found to amount to about 80 per cent. of

the raw material. The benzoin contains traces of a volatile oil, and a

substance soluble in water, at least through the agency of carbonate of

potash. Ether does not dissolve benzoin completely. The fat and volatile

oils dissolve very little of it.

Unverdorben has found in benzoin, besides benzoic acid, and a little

volatile oil, no less than three different kinds of resin, none of which

has, however, been turned as yet to any use in the arts.

Benzoin is of great use in perfumery, as it enters into a number of

preparations; among which may be mentioned fumigating pastilles,

fumigating cloves (called also nails), _poudre à la maréchale_, &c. The

alcoholic tincture, mixed with water, forms _virginal_ milk. Benzoin

enters also into the composition of certain varnishes employed for

snuff-boxes and walkingsticks, in order to give these objects an

agreeable smell when they become heated in the hand. It is likewise

added to the spirituous solution of isinglass with which the best court

plaster is made.

BERLIN BLUE. Prussian blue. See BLUE.

BERRIES OF AVIGNON, _and Persian Berries_. (_Graines d’Avignon_, Fr.;

_Gelbbeeren_, Germ.) A yellowish dye-drug, the fruit of the _rhamnus

infectorius_, a plant cultivated in Provence, Languedoc, and Dauphiné,

for the sake of its berries, which are plucked before they are ripe,

while they have a greenish hue. Another variety comes from Persia,

whence its trivial name; it is larger than the French kind, and has

superior properties. The principal substances contained in these berries

are: 1. A colouring matter, which is united with a matter insoluble in

ether, little soluble in concentrated alcohol, and very soluble in

water: it appears to be volatile. 2. A matter remarkable for its

bitterness, which is soluble in water and alcohol. 3. A third principle,

in small quantity. A decoction of one part of the Avignon or Persian

berry in ten of water affords a brown-yellow liquor bordering upon

green, having the smell of a vegetable extract, and a slightly bitter

taste.

With gelatine that decoction gives, after some time, a slight

precipitate,--

With alkalies a yellow hue,

-- acids a slight muddiness,

-- lime-water a greenish-yellow tint,

-- alum a yellow colour,

-- red sulphate of iron an olive-green colour,

-- sulphate of copper an olive colour,

-- proto-muriate of tin a greenish yellow with a slight

precipitate. (See CALICO PRINTING.)

BERYL. A beautiful mineral or gem, of moderate price, usually of a green

colour of various shades, passing into honey-yellow and sky blue.

BEZOAR. The name of certain concretions found in the stomachs of

animals, to which many fanciful virtues were formerly ascribed. They are

interesting only to the chemical pathologist.

BILE. (_Bile_, Fr.; _Galle_, Germ.) The secreted liquor of the liver in

animals. For an account of the uses of animal bile in the arts, see

GALL.

BIRDLIME. (_Glu_, Fr.; _Vogelleim_, Germ.) The best birdlime may be made

from the middle bark of the holly, boiled seven or eight hours in water,

till it is soft and tender, then laid by heaps in pits under ground,

covered with stones after the water is drained from it. There it must be

left during two or three weeks, to ferment in the summer season, and

watered, if necessary, till it passes into a mucilaginous state. It is

then to be pounded in a mortar to a paste, washed in running water, and

kneaded till it be free from extraneous matters. It is next left for

four or five days in earthen vessels to ferment and purify itself, when

it is fit for use. Birdlime may be made by the same process from the

mistletoe (_viburnum lantana_), young shoots of elder, and the barks of

other vegetables, as well as from most parasite plants.

Good birdlime is of a greenish colour, and sour flavour, somewhat

resembling that of linseed oil; gluey, stringy, and tenacious. By drying

in the air it becomes brittle, and may be powdered; but its viscosity

may be restored by moistening it. It has an acid reaction with litmus

paper. It contains resin, mucilage, a little free acid, colouring and

extractive matter. The resin has been called VISCINE.

BISMUTH. (_Bismuth_, Fr.; _Wismuth_, Germ.) Called also marcasite and

tin-glass. It was shown to be a metal somewhat different from lead, by

G. Agricola, in 1546; Stahl and Dufay proved its peculiarity; but it was

more minutely distinguished by Pott and Geoffroy, about the middle of

the last century. It is a rare substance, occurring native, as an oxide,

under the name of bismuth ochre; as a sulphuret, called bismuth glance;

as a sulphuret with copper, called copper bismuth ore; as also with

copper and lead, called needle ore. It is found associated likewise with

selenium and tellurium. The native metal occurs in various forms and

colours, as white, reddish, and variegated; in primitive and floetz

formations, along with the ores of cobalt, nickel, copper, silver, and

bismuth ochre; at the Saxon Erzgebirge, near Schneeberg, and Joh.

Georgenstadt; also in Bohemia, Baden, Wurtemberg, Hessia, Sweden,

Norway, England, and France.

The production of this metal is but a limited object of the

smelting-works of the Saxon Erzgebirge at Schneeberg. It there occurs,

mixed with cobalt speiss, in the proportion of about 7 per cent. upon

the average, and is procured by means of a peculiar furnace of

liquation, which is the most economical method, both as to saving fuel,

and oxidisement of the bismuth.

[Illustration: 112 113 114]

The bismuth eliquation furnace at Schneeberg is represented in _figs._

112, 113, and 114., of which the first is a view from above, the second

a view in front, and the third a transverse section in the dotted line A

B of _fig._ 112. _a_ is the ash-pit; _b_, the fireplace; _c_, the

eliquation pipes; _d_, the grate of masonry or brickwork, upon which the

fuel is thrown through the fire-door _e e_. The anterior deeper lying

orifice of the eliquation pipes is closed with the clay-plate _f_; which

has beneath a small circular groove, through which the liquefied metal

flows off. _g_ is a wall extending from the hearth-sole nearly to the

anterior orifices of the eliquation pipes, in which wall there are as

many fire-holes, _h_, as there are pipes in the furnace; _i_ are iron

pans, which receive the fluid metal; _h_, a wooden water-trough, in

which the bismuth is granulated and cooled; _l_, the posterior and

higher lying apertures of the eliquation pipes, shut merely with a

sheet-iron cover. The granulations of bismuth drained from the posterior

openings fall upon the flat surfaces _m_, and then into the

water-trough. _n n_ are draught-holes in the vault between the two

pipes, which serve for increasing or diminishing the heat at pleasure.

The ores to be eliquated (sweated) are sorted by hand from the gangue,

broken into pieces about the size of a hazel nut, and introduced into

the ignited pipes; one charge consisting of about 1/2 cwt.; so that the

pipes are filled to half their diameter, and three fourths of their

length. The sheet-iron door is shut, and the fire strongly urged,

whereby the bismuth begins to flow in ten minutes, and falls through the

holes in the clay-plates into hot pans containing some coal-dust.

Whenever it runs slowly, the ore is stirred round in the pipes, at

intervals during half an hour, in which time the liquation is usually

finished. The residuum, called bismuth barley (_graupen_), is scooped

out with iron rakes into a water trough; the pipes are charged afresh;

the pans, when full, have their contents cast into moulds, forming bars

of from 25 to 50 pounds weight. About 20 cwt. of ore are smelted in 8

hours, with a consumption of 63 Leipzic cubic feet of wood. The total

production of Schneeberg, in 1830, was 9800 lbs. The bismuth thus

procured by liquation upon the great scale, contains no small admixture

of arsenic, iron, and some other metals, from which it may be freed by

solution in nitric acid, precipitation by water, and reduction of the

subnitrated oxide by black flux. By exposing the crude bismuth for some

time to a dull red heat, under charcoal, arsenic is expelled.

Bismuth is white, and resembles antimony, but has a reddish tint;

whereas the latter metal has a bluish cast. It is brilliant,

crystallises readily in small cubical facets, is very brittle, and may

be easily reduced to powder. Its specific gravity is 9·83; and by

hammering it with care, the density may be increased to 9·8827. It melts

at 480° Fahr., and may be cooled 6 or 7 degrees below this point without

fixing; but the moment it begins to solidify, the temperature rises to

480°, and continues stationary till the whole mass is congealed. When

heated from 32° to 212°, it expands 1/710 in length. When pure it

affords a very valuable means of adjusting the scale of high-ranged

thermometers. At strong heats bismuth volatilises, may be distilled in

close vessels, and is thus obtained in crystalline laminæ.

The alloy of bismuth and lead in equal parts has a density of 10·709,

being greater than the mean of the constituents; it has a foliated

texture, is brittle, and of the same colour as bismuth. Bismuth, with

tin, forms a compound more elastic and sonorous than the tin itself, and

is therefore frequently added to it by the pewterers. With 1 of bismuth

and 24 of tin, the alloy is somewhat malleable; with more bismuth, it is

brittle. When much bismuth is present, it may be easily parted by strong

muriatic acid, which dissolves the tin, and leaves the bismuth in a

black powder. It has been said, that an alloy of tin, bismuth, nickel,

and silver, hinders iron from rusting. (_Erdmann’s Journal._) The alloy

of bismuth with tin and lead was first examined by Sir I. Newton, and

has been called ever since fusible metal. Eight parts of bismuth, 5 of

lead, and 3 of tin, melt at the moderate temperature of 202° F.; but 2

of bismuth, 1 of lead, and 1 of tin, melt at 200·75° F. according to

Rose. A small addition of mercury of course aids the fusibility. Such

alloys serve to take casts of anatomical preparations. An alloy of 1

bismuth, 2 tin, and 1 lead, is employed as a soft solder by the

pewterers; and the same has been proposed as a bath for tempering steel

instruments. Cake-moulds, for the manufacturers of toilet soaps are made

of the same metal; as also excellent clichés for stereotype, of 3 lead,

2 tin, and 5 bismuth; an alloy which melts at 199° F. This compound

should be allowed to cool upon a piece of pasteboard, till it becomes of

a doughy consistence, before it is applied to the mould, to receive the

impress of the stamp.

The employment of plates of fusible metal as safety _rondelles_, to

apertures in the tops of steam boilers has been proposed in France,

because they would melt and give way at elevations of temperature under

those which would endanger the bursting of the vessel; the fusibility of

the alloy being proportioned to the quality of steam required for the

engine. It has been found, however, that boilers, apparently secured in

this way, burst, while the safety discs remained entire; the expansive

force of the steam causing explosion so suddenly, that the fusible alloy

had not time to melt or give way.

There are two, perhaps three, oxides of bismuth; the first and the

third, or the suboxide and super-oxide, are merely objects of chemical

curiosity. The oxide proper occurs native, and may be readily formed by

exposing the metal to a red-white heat in a muffle, when it takes fire,

burns with a faint blue flame, and sends off fumes which condense into a

yellow pulverulent oxide. But an easier process than that now mentioned

is to dissolve the bismuth in nitric acid, precipitate with water, and

expose the precipitate to a red heat. The oxide thus obtained has a

straw yellow colour, and fuses at a high heat into an opaque glass of a

dark-brown or black colour; but which becomes less opaque and yellow

after it has cooled. Its specific gravity is so high as 8·211. It

consists of 89·87 of metal and 10·13 oxygen in 100 parts. The above

precipitate, which is a sub-nitrate of bismuth, is called _pearl-white_,

and is employed as a flux for certain enamels; as it augments their

fusibility without imparting any colour to them. Hence, it is used

sometimes as a vehicle of the colours of other metallic oxides. When

well washed, it is employed in gilding porcelain; being added in the

proportion of one fifteenth to the gold. But pearl-white is most used by

ladies, as a cosmetic for giving a brilliant tint to a faded complexion.

It is called _blanc de fard_, by the French. If it contains, as bismuth

often does, a little silver, it becomes grey or dingy coloured on

exposure to light. When the oxide is prepared, by dropping the nitric

solution into an alkaline lye in excess, if this precipitate is well

washed and dried, it forms an excellent medicine; and is given, mixed

with gum tragacanth, for the relief of cardialgia, or burning and

spasmodic pains of the stomach.

Another sort of pearl-powder is prepared by adding a very dilute

solution of common salt to the above nitric solution of bismuth, whereby

a pulverulent sub-chloride of the metal is obtained in a light

flocculent form. A similar powder of a mother-of-pearl aspect may be

formed by dropping dilute muriatic acid into the solution of nitrate of

bismuth. The arsenic always present in the bismuth of commerce is

converted by nitric acid into arsenic acid, which, forming an insoluble

arseniate of bismuth, separates from the solution, unless there be such

an excess of nitric acid as to re-dissolve it. Hence the medicinal

oxide, prepared from a rightly-made nitrate, can contain no arsenic. If

we write with a pen dipped in that solution, the dry invisible traces

will become legible on plunging the paper in water.

It has been proposed to substitute bismuth for lead in assaying silver,

as a smaller quantity of it answers the purpose, and, as its oxide is

more fluent, can therefore penetrate the cupel more readily, and give a

more rapid result. But, independently of the objection from its high

price, bismuth has the disadvantage of boiling up, as well as of

_rocking_ or vegetating, with the silver, when the cupellation requires

a high heat. In extracting the silver from the galena found in the

copper-mine of Yahlun, it has happened sometimes that the silver

concreted towards the end of the operation, and produced a cauliflower

excrescence, which had to be cupelled again with a fresh dose of lead.

It was observed that, in this case, a portion of the silver had passed

into the cupel. Berzelius detected in a sample of silver thus concreted

the presence of bismuth.

The nitrate of bismuth, mixed with solution of tin and tartar, has been

employed as a mordant for dyeing lilac and violet in calico printing.

BISTRE. (_Bistre_, Fr. _bister_, Germ.) A brown colour which is used in

water colours, in the same way as China ink. It is prepared from

wood-soot, that of beech being preferred. The most compact and best

burned parcels of soot are collected from the chimney, pulverised, and

passed through a silk sieve. This powder is infused in pure water, and

stirred frequently with a glass ruler, then allowed to settle when the

water is decanted. If the salts are not all washed away, the process may

be repeated with warm water. The paste is now to be poured into a long

narrow vessel filled with water, stirred well, and left to settle for a

few minutes, in order to let the grosser parts subside. The supernatant

part is then to be poured off into a similar vessel. This process may be

repeated twice or thrice, to obtain a very good bistre. At last the

settled deposit is sufficiently fine, and, when freed from its

supernatant water, it is mixed with gum-water, moulded into proper

cakes, and dried. It is not used in oil painting, but has the same

effect in water-colours as brown pink has in oil.

BITUMEN, or ASPHALTUM. (_Bitume_, Fr. _Erdpech_, Germ.) A black

substance found in the earth, externally not dissimilar to pit-coal. It

is composed of carbon, hydrogen, and oxygen, like organic bodies; but

its origin is unknown. It has not been observed among the primitive or

older strata, but only in the secondary and alluvial formations. It

constitutes sometimes considerable beds, as in the isle of Trinidad,

where it occurs over an extensive district, in scattered masses. The

greater part of the asphaltum to be met with in commerce comes from the

Dead Sea, on whose shores it is cast up and gathered; whence it has got

the name of Jewish bitumen. In its black colour and fracture it

resembles ordinary pitch. By friction it affords negative electricity.

Its average density is 1·16. It melts at the temperature of boiling

water, kindles very readily at the flame, burns brightly with a thick

smoke, and leaves little ashes. Distilled by itself, it yields a

peculiar bituminous oil, very little water, some combustible gases, and

traces of ammonia. It leaves about one third of its weight of charcoal

after combustion, and ashes, containing silica, alumina, oxide of iron,

sometimes a little lime, and oxide of manganese. According to John,

asphaltum may be decomposed, by different solvents, into three distinct

substances. Water dissolves nothing; alcohol (anhydrous) dissolves out a

yellow resin equal to 5 per cent. of the weight of the asphaltum; that

resin is soluble in dilute alcohol and in ether. The portion not soluble

in the alcohol gives up a brown resin to ether, amounting to 70 per

cent. of the weight of the asphaltum. On evaporating off the ether, the

resin remains of a brownish-black colour, which dissolves readily in the

volatile oils and in the oil of petroleum. The portion of asphaltum

which does not dissolve in ether is very soluble in oil of turpentine,

and in oil of petroleum; but less so in oil of lavender. These three

resinous principles dissolve all together by digestion in the oils of

anise, rosemary, turpentine, olive, hemp-seed, nut, and linseed. Caustic

potash dissolves a notable quantity of asphaltum; but carbonate of

potash has no effect upon it.

Asphaltum enters into the composition of hydraulic cements, and into

that of black varnishes, called japans, for coating iron trays, &c. A

similar varnish may be prepared by dissolving 12 parts of fused amber, 2

parts of rosin, and 2 parts of asphaltum, in 6 parts of linseed oil

varnish, to which 12 parts of oil of turpentine have been added.

There is a kind of bitumen found at Aniches, in France, in the

department of the north, which is black, very fusible, and soft. It

burns with flame. Alcohol, ether, and oil of turpentine extract from it

a fatty substance, which may be saponified with alkalis.

The bitumen of Murindò, near Choco, in Columbia, is of a brownish-black

colour, soft, and has an earthy fracture. It has an acrid taste, burns

with a smell of vanilla, and is said to contain a large quantity of

benzoic acid. It appears to be the result of the decomposition of trees

containing benzoin.

Asphaltum occurs abundantly at the surface of the salt lake Asphaltites,

in Judea, produced from springs in the neighbourhood; it is floated

down, gathers consistence, and accumulates upon the surface of the lake;

the winds drive it on the shores, and the inhabitants collect it for

sale. Its inspissation diffuses a disagreeable smell in the air of that

region, which is supposed by the natives to be powerful enough to kill

birds when they attempt to fly across the lake.

But probably the most remarkable locality of asphaltum in the world is

the entire basin, or rather plain of it, in the island of Trinidad,

called the Tar Lake. It lies on the highest land in the island, and

emits a strong smell, sensible at ten miles’ distance. Its first

appearance is that of a lake of water, but, when viewed more nearly, it

seems to be a surface of glass. In hot weather its surface liquifies to

the depth of an inch, and it cannot then be walked upon. It is of a

circular form, about three miles in circumference, and of a depth not

ascertained. Large fissures frequently open and close up in it, whence

the pitch has been supposed to float upon a body of water. The soil, for

a considerable distance round it, consists of cinders and burnt earth,

and presents in many points indications of convulsions by subterranean

fire. In several parts of the neighbouring woods, there are round holes

and fissures in the ground, containing liquid bitumen to the depth of

two inches.

Mr. Hatchett examined some specimens from Trinidad, and concluded that

what had been heretofore supposed to be a pure mineral pitch was in

reality only a porous stone of the argillaceous kind, much impregnated

with bitumen.

These various bitumens belong exclusively to the secondary and tertiary

geological formations, and are not found among primitive rocks, except

very rarely in veins. They occur most generally in calcareous,

argillaceous, and sandy strata, and also in volcanic districts.

Petroleum frequently floats on the waters which issue from the volcanic

mountains, or which lie at their base; even the sea is at times covered

with it near the volcanic islands of Cape Verd. Mr. Breislak observed a

petroleum spring rising from the bottom of the sea near the southern

base of Vesuvius.

The substance with which bitumen seems to have the most constant and

most remarkable relations, is sea-salt; so that almost all the countries

most abundant in petroleum, as Italy, Transylvania, Persia, the environs

of Babylon, the region of the Dead Sea, &c., contain salt mines, or

lakes, or exhibit saline efflorescences. Iron pyrites is often

impregnated with petroleum, or contains a bituminous nucleus.

The origin of bitumen is as little known as that of most of the

productions of nature. Some regard it as an empyreumatic oil, a matter

analogous to liquid resin or essential oil, resulting from the

destruction of that astonishing multitude of animals and vegetables

buried in the earth, whose solid remains are daily brought to view in

mineral researches. It has been also supposed that naphtha and petroleum

are the product of coals decomposed either by the fire of volcanos, by

the subterranean combustion of coal itself, or by the decomposition of

pyrites. The latter opinion is not supported by any direct evidence, but

the two former are sufficiently probable.

_Elastic Bitumen_ is a rare substance, found hitherto only near

Castleton, in Derbyshire, in fissures of slaty clay.

_Bituminous mastic, or cement_, has been of late extensively employed in

France for covering roofs and terraces, and lining water cisterns. The

mineral bitumen used for the composition of this mastic is procured

chiefly from the _Obsann_ (Bas-Rhin), from the Parc (department de

l’Ain), and from the _Puy-de-la-Poix_ (department of Puy-de-Dome). But

boiled coal-tar answers equally well. In the neighbourhood of these

localities, there is a limestone impregnated with bitumen, which suits

for giving consistence to the cement. This is well dried, ground to

powder, sifted, and stirred while hot, in about one fifth its weight of

melted asphaltum, contained in a cast-iron boiler. Dry chalk or bricks,

ground and sifted, will suit equally well. As soon as this paste is made

quite homogeneous, it is lifted out with an iron shovel or spoon, and

spread in rectangular moulds, secured with pegs at the joints, fastened

to a kind of platform of smoothed planks, covered with strong

sheet-iron. The sides of these moulds should be previously smeared over

with a thin coat of loam-paste, to prevent their adhesion to the mastic.

Whenever the cake is cold, the frame is taken asunder, and it is removed

from the iron plate by an oblong shovel, or strong spatula of iron.

These cakes or bricks are usually 18 inches long, 12 broad, and 4 thick,

and weigh about 70 lbs.

BITTER PRINCIPLE. (_Amère_, Fr.; _Bitterstoff_, Germ.) This principle

has not been insulated hitherto by the chemist from the other proximate

principles of plants, but its existence is sufficiently recognised by

the taste. The following list contains the principal bitter substances,

many of which have been used in the arts and in medicine.

+--------------+-----------------+------------------+--------------+

+--------------+-----------------+------------------+--------------+

|Orange |Unripe fruit |South of Europe } |Aromatic |

|Ditto |Peel |Ditto } |bitter |

+--------------+-----------------+------------------+--------------+

BLACK DYE. (_Teinte noire_, Fr. _Schwartze farbe_, Germ.) For 1 cwt. of

cloth, there are put into a boiler of middle size 18 lbs. of logwood,

with as much Aleppo galls in powder, and the whole, being enclosed in a

bag, is boiled in a sufficient quantity of water for 12 hours. One-third

of this bath is transferred into another boiler with two pounds of

verdigris; and the stuff is passed through this solution, stirring it

continually during two hours, taking care to keep the bath very hot

without boiling. The stuff is then lifted out, another third of the bath

is added to the boiler, along with eight pounds of sulphate of iron or

green vitriol. The fire is to be lowered while the sulphate dissolves,

and the bath is allowed to cool for half an hour, after which the stuff

is introduced, and well moved about for an hour, after which it is taken

out to air. Lastly, the remaining third of the bath is added to the

other two, taking care to squeeze the bag well. 18 or 22 lbs. of sumach

are thrown in; the whole is just brought to a boil, and then refreshed

with a little cold water; two pounds more of sulphate of iron are added,

after which the stuff is turned through for an hour. It is thereafter

washed, aired, and put again into the bath, stirring it continually for

an hour. After this, it is carried to the river, washed well, and then

filled. Whenever the water runs off clear, a bath is prepared with weld,

which is made to boil for an instant; and after refreshing the bath the

stuff is turned in to soften, and to render the black more fast. In this

manner, a very beautiful black is obtained, without rendering the cloth

too harsh.

Commonly more simple processes are employed. Thus the blue cloth is

simply turned through a bath of gall-nuts, where it is boiled for two

hours. It is next passed through a bath of logwood and sulphate of iron

for two hours, without boiling, after which it is washed and fulled.

Hellot has found that the dyeing might be performed in the following

manner:--For 20 yards of dark blue-cloth, a bath is made of two pounds

of fustic (morus tinctoria), 4-1/4 lbs. of logwood, and 11 lbs. sumach.

After boiling the cloth in it for three hours it is lifted out, 11 lbs.

of sulphate of iron are thrown into the boiler, and the cloth is then

passed through it during two hours. It is now aired, and put again in

the bath for an hour. It is, lastly, washed and scoured. The black is

less velvety than that of the preceding process. Experience convinced

him that the maddering prescribed in the ancient regulations only gives

a reddish cast to the black, which is obtained finer and more velvety

without madder.

A black may be dyed likewise without having given a blue ground. This

method is employed for cloths of little value. In this case they are

rooted; that is to say, they receive a dun ground with walnut husks, or

the root of the walnut tree, and are afterwards made black in the manner

above described, or in some other way; for it is obvious that a black

may be obtained by several processes.

According to Lewis, the proportions which the English dyers most

generally adopt are, for one hundred and twelve pounds of woollen cloth

previously dyed of a dark blue, about five pounds of sulphate of iron,

as much gall-nuts, and thirty pounds of logwood. They begin by galling

the cloth, they then pass it through the decoction of logwood, to which

the sulphate of iron has been added.

When the cloth is completely dyed, it is washed in the river, and passed

through the fulling-mill till the water runs off clear and colourless.

Some persons recommend, for fine cloths, to full them with soap water.

This operation requires an expert workman, who can free the cloth

thoroughly from the soap. Several recommend at its coming from the

fulling to pass the cloth through a bath of weld, with the view of

giving softness and solidity to the black. Lewis says, that passing the

cloth through weld, after it has been treated with soap, is absolutely

useless, although it may be beneficial when this operation has been

neglected.

Different operations may be distinguished in dyeing _silk_ black; the

boiling of the silk, its galling, the preparation of the bath, the

operation of dyeing, the softening of the black.

Silk naturally contains a substance called gum, which gives it the

stiffness and elasticity peculiar to it in its native state; but this

adds nothing to the strength of the silk, which is then styled raw; it

rather renders it, indeed, more apt to wear out by the stiffness which

it communicates; and although raw silk more readily takes a black

colour, yet the black is not so perfect in intensity, nor does it so

well resist the re-agents capable of dissolving the colouring particles,

as silk, which is scoured or deprived of its gum.

To cleanse silk intended for black, it is usually boiled four or five

hours with one fifth of its weight of white soap, after which it is

carefully beetled and washed.

For the galling, nut-galls equal nearly to three fourths of the weight

of the silk are boiled during three or four hours; but on account of the

price of Aleppo galls, more or less of the white gall-nuts, or of even

an inferior kind called galon, berry or apple galls, are used. The

proportion commonly employed at Paris is two parts of Aleppo galls to

from eight to ten parts of galon. After the boiling, the galls are

allowed to settle for about two hours. The silk is then plunged into the

bath, and left in it from twelve to thirty-six hours, after which it is

taken out and washed in the river.

Silk is capable of combining with quantities, more or less considerable,

of the astringent principle; whence results a considerable increase of

weight, not only from the weight of the astringent principle, but also

from that of the colouring particles, which subsequently fix themselves

in proportion to the quantity of the astringent principle which had

entered into combination. Consequently, the processes are varied

according to the degree of weight which it is wished to communicate to

the silk; a circumstance requiring some illustration.

The commerce of silk goods is carried on in two ways; they are sold

either by the weight, or by the surface, that is, by measure. Thus the

trade of Tours was formerly distinguished from that of Lyons; the silks

of the former being sold by weight, those of the latter, by measure. It

was therefore their interest to surcharge the weight at Tours, and, on

the contrary, to be sparing of the dyeing ingredients at Lyons; whence

came the distinction of light black and heavy black. At present, both

methods of dyeing are practised at Lyons, the two modes of sale having

been adopted there.

Silk loses nearly a fourth of its weight by a thorough boiling, and it

resumes, in the light black dye, one half of this loss; but in the heavy

black dye, it takes sometimes upwards of a fifth more than its primitive

weight; a surcharge injurious to the beauty of the black, and the

durability of the stuff. The surcharged kind is denominated English

black, because it is pretended that it was first practised in England.

Since silk dyed with a great surcharge has not a beautiful black, it is

usually destined for weft, and is blended with a warp dyed of a fine

black.

The peculiarity of the process for obtaining the heavy black consists in

leaving the silk longer in the gall liquor, in repeating the galling, in

passing the silk a greater number of times through the dye, and even

letting it lie in it for some time. The first galling is usually made

with galls which have served for a preceding operation, and fresh

gall-nuts are employed for the second. But these methods would not be

sufficient for giving a great surcharge, such as is found in what is

called the English black. To give it this weight, the silk is galled

without being ungummed; and, on coming out of the galls, it is rendered

supple by being worked on the jack and pin.

The silk-dyers keep a black vat, and its very complex composition varies

in different dye-houses. These vats are commonly established for many

years; and when their black dye is exhausted it is renovated by what is

called in France a _brevet_. When the deposit which has accumulated in

it is too great, it is taken out, so that at the end of a certain time

nothing remains of the several ingredients which composed the primitive

bath, but which are not employed in the brevet.

For the dyeing of raw silk black, it is galled in the cold, with the

bath of galls which has already served for the black of boiled silk. For

this purpose, silk, in its native yellow colour, is made choice of. It

should be remarked, that when it is desired to preserve a portion of the

gum of the silk, which is afterwards made flexible, the galling is given

with the hot bath of gall-nuts in the ordinary manner. But here, where

the whole gum of the silk, and its concomitant elasticity, are to be

preserved, the galling is made in the cold. If the infusion of galls be

weak, the silk is left in it for several days.

Silk thus prepared and washed takes very easily the black dye, and the

rinsing in a little water, to which sulphate of iron may be added, is

sufficient to give it. The dye is made in the cold; but, according to

the greater or less strength of the rinsings, it requires more or less

time. Occasionally three or four days are necessary; after which it is

washed, it is beetled once or twice, and it is then dried without

wringing, to avoid softening it.

Raw silk may be more quickly dyed, by shaking it round the rods in the

cold bath after the galling, airing it, and repeating these

manipulations several times, after which it is washed and dried as

above.

Macquer describes a more simple process for the black by which velvet is

dyed at Genoa; and he says that this process, rendered still simpler,

has had complete success at Tours. The following is his description.

For 1 cwt. (50 kilogrammes) silk, (22 lbs. 11 kilogrammes) of Aleppo

galls, in powder, are boiled for an hour in a sufficient quantity of

water. The bath is allowed to settle till the galls have fallen to the

bottom of the boiler, from which they are withdrawn; after which 32 lbs.

of English vitriol (or copperas) are introduced, with 13 lbs. of iron

filings, and 22 lbs. of country gum, put into a kind of two-handled

cullender, pierced every where with holes. This kettle is suspended by

two rods in the boiler, so as not to reach the bottom. The gum is left

to dissolve for about an hour, stirring it from time to time. If, after

this time, some gum remains in the kettle, it is a proof that the bath,

which contains two hogsheads, has taken as much of it as is necessary.

If, on the contrary, the whole gum is dissolved, from one to 4 lbs. more

may be added. This cullender is left constantly suspended in the boiler,

from which it is removed only when the dyeing is going on; and

thereafter it is replaced. During all these operations the boiler must

be kept hot, but without boiling. The galling of the silk is performed

with one third of Aleppo galls. The silk is left in it for six hours

the first time, then for twelve hours. The rest, _secundum artem_.

Lewis states that he has repeated this process in the small way; and

that, by adding sulphate of iron progressively, and repeating the

immersions of the silk a great number of times, he eventually obtained a

fine black.

Astringents differ from one another as to the quantity of the principle

which enters into combination with the oxide of iron. Hence, the

proportion of the sulphate, or of any other salt of iron, and that of

the astringents, should vary according to the astringents made use of,

and according to their respective quantities. Gall-nut is the substance

which contains most astringent; sumach, which seems second to it in this

respect, throws down (decomposes), however, only half as much sulphate

of iron.

The most suitable proportion of sulphate of iron appears to be that

which corresponds to the quantity of the astringent matter, so that the

whole iron precipitable by the astringent may be thrown down, and the

whole astringent may be taken up in combination with the iron. As it is

not possible, however, to arrive at such precision, it is better that

the sulphate of iron should predominate, because the astringent, when in

excess, counteracts the precipitation of the black colouring particles,

and has the property of even dissolving them.

This action of the astringent is such that, if a pattern of black cloth

be boiled with gall-nuts, it is reducible to grey. An observation of

Lewis may thence be explained. If cloth be turned several times through

the colouring bath, after it has taken a good black colour, instead of

acquiring more body, it is weakened, and becomes brownish. Too

considerable a quantity of the ingredients produces the same effect; to

which the sulphuric acid, set at liberty by the precipitation of the

oxide of iron, contributes.

It is merely the highly oxidised sulphate which is decomposed by the

astringent; whence it appears, that the sulphate will produce a

different effect according to its state of oxidisement, and call for

other proportions. Some advise, therefore, to follow the method of

Proust, employing it in the oxidised state; but in this case it is only

partially decomposed, and another part is brought, by the action of the

astringent, into the lower degree of oxidisement.

The particles precipitated by the mixture of an astringent and sulphate

of iron have not at first a deep colour; but they pass to a black by

contact of air while they are moist.

Under _dyeing_ I shall show that the black dye is only a very condensed

colour, and that it assumes more intensity from the mixture of different

colours likewise deep. It is for this reason advantageous to unite

several astringents, each combination of which produces a different

shade. But blue appears the colour most conducive to this effect, and it

corrects the tendency to dun, which is remarked in the black produced on

stuffs by the other astringents.

On this property is founded the practice of giving a blue ground to

black cloths, which acquire more beauty and solidity the deeper the

blue. Another advantage of this practice is to diminish the quantity of

sulphuric acid which is necessarily disengaged by the precipitation of

the black particles, and which would not only counteract their fixation,

but would further weaken the stuff, and give it harshness.

For common stuffs, a portion of the effect of the blue ground is

produced by the rooting.

The mixture of logwood with astringents contributes to the beauty of the

black in a twofold way. It produces molecules of a hue different from

what the astringents do, and particularly blue molecules, with the oxide

of copper, commonly employed in the black dyes; which appears to be more

useful the more acetate the verdigris made use of contains.

The boil of weld, by which the dye of black cloth is frequently

finished, may also contribute to its beauty, by the shade peculiar to

its combination. It has, moreover, the advantage of giving softness to

the stuffs.

The processes that are employed for wool, yield, according to the

observation of Lewis, only a rusty black to silk; and cotton is hardly

dyed by the processes proper for wool and silk. Let us endeavour to

ascertain the conditions which these three varieties of dyeing demand.

Wool has a great tendency to combine with colouring substances; but its

physical nature requires its combinations to be made in general at a

high temperature. The combination of the black molecules may therefore

be directly effected in a bath, in proportion as they form; and, if the

operation be prolonged by subdividing it, it is only with the view of

changing the necessary oxidisement of the sulphate, and augmenting that

of the colouring particles themselves.

Silk has little disposition to unite with the black particles. It seems

to be merely by the agency of the tannin, with which it is previously

impregnated, that these particles can fix themselves on it, especially

after it has been scoured. For this reason, silk baths should be old,

and have the colouring particles accumulated in them, but so feebly

suspended as to yield to a weak affinity. Their precipitation is

counteracted by the addition of gum, or other mucilaginous substances.

The obstacle which might arise from the sulphuric acid set at liberty is

destroyed by iron filings, or other basis. Thus, baths of a very

different composition, but with the essential condition of age, may be

proper for this dye. For cotton black dye, see CALICO PRINTING.

BLACK PIGMENT. The finest light black is prepared principally for the

manufacturing of printers’ ink. In Messrs. Martin and Grafton’s patent

process, the black is obtained by burning common coal-tar, which should,

however, be previously divested, as much as possible, of the ammoniacal

liquor and acid mixed with it in the tank.

For this purpose, it is proposed that four casks should be employed,

each capable of holding 130 gallons, and into every one of them are to

be put about 60 gallons of the rough impure tar, to which an equal

quantity of lime-water is to be added, and then agitated by machinery or

manual labour until the lime-water is completely mixed with the tar. The

vessels should next be suffered to rest for about six hours, by which

time the tar will settle at the bottom of the casks, and the water may

be drawn off. The casks containing the tar should now be filled with hot

water, which may be supplied from the boiler of a steam engine, and the

whole again agitated as before. This process may be repeated three

times, suffering the tar to subside between each; and twelve hours

should be allowed for settling from the last water, so that the whole of

the tar and water may become separated, the water rising to the top of

the cask, and the tar being left at the bottom in a pure state.

But, as some of the water will yet remain mechanically combined with the

tar, it is proposed that the tar should be subjected to the process of

distillation. For this purpose, a still, capable of holding 120 gallons,

may be employed, in which about 50 gallons, at one time, may be operated

upon; when, by a gentle heat, the water, and other impurities which the

tar may have retained, will be driven off. As soon as the water appears

to have evaporated, and the spirit runs fine and clear, the process of

distillation should be stopped; and, when cold, the pure tar may be

drawn off, and set apart for the purpose of being employed as

contemplated in the patent.

The tar thus purified may be now converted into black, or it may be

subjected to further rectification to divest it of the mineral pitch, or

asphaltum, which is combined with the oil and spirit: the latter is to

be preferred, because the mineral pitch, or asphaltum, is only

inflammable at a high temperature, which renders it more troublesome to

use in the process here contemplated, and also would cause the apparatus

to require frequent cleaning from the carbonized pitch deposited. In

order, therefore, to get rid of the mineral pitch, or asphaltum, forty

gallons of the tar are to be introduced into a still, as before; and,

instead of stopping the operation, as soon as the spirit begins to come

over, the distillation is continued with a strong heat, so as to force

over the whole of the oil and spirit, leaving the residuum of asphaltum

in the still: this process, however, is known to every chemist, and need

not be further explained.

[Illustration: 115 116]

In _fig._ 115. is exhibited a rude representation of the apparatus

employed in preparing and collecting the fine light spirit black,

produced by the combustion of the oil and spirit of coal-tar, after it

has been purified as above described. _a_ is the brickwork which

supports a number of burners issuing from a tube, _b_, within, and here

shown by dots, as passing along its whole length. _Fig._ 116. is a

section of the brickwork, with the tube, burner, and receiver, as will

be described hereafter. The tube may be called the tar main, as it is

intended to be filled with tar: it is constructed of cast iron, and from

it issue several (in this figure twenty-four) jets or burners, _c_, _c_,

_c_; any other number may be employed. _d_ is a furnace under the tar

main, the flue of which extends along, for the purpose of heating the

tar to the boiling point, in order to facilitate the process. From the

main, _b_, the tar flows into the jets _c_; wicks are introduced into

the jets, and, when set fire to by a red-hot stick, will burn and emit a

very considerable quantity of smoke; which it is the object of this

apparatus to conduct through many passages, for the purpose of

collecting its sooty particles.

There are a number of hoods, _e_, _e_, _e_, or bonnets, as they are

termed, all of which, through their pipes, have communication with, or

lead into, a main chimney, _f_, _f_. Into these hoods or bonnets the

smoke of the burners ascends, and from thence passes into the main

chimney _f_, and thence through the smoke tubes into the box _g_: here

the heaviest particles of the black deposit themselves; but, as the

smoke passes on through the farther pipes, a deposit of the second, or

finer, particles of black takes place in the box _h_. From hence the

smoke proceeds through other pipes into a series of canvass bags, _i_,

_i_, _i_, which are proposed to be about eighteen feet long, and three

in diameter. These bags are connected together at top and bottom

alternately, and through the whole series the smoke passes up one bag

and down the next, depositing fine black, called spirit black, upon the

sides of the canvass. After the jets have continued burning for several

days, the bags are to be beaten with a stick, so that the black may fall

to the bottom; and, when a sufficient quantity has accumulated, the bags

may be emptied and swept out. Thus seventy or eighty bags may be

employed; so that the smoke should pass through a length of about 400

yards, the farthest of which will be found to contain the finest black.

The last bag should be left open, in order to allow the vapour to escape

into the open air.

The main tar tube will require to be emptied every four or five days, in

order to clear it from the pitchy matter that may have subsided from the

burners, and they also will require to be frequently poked with a wire,

to clear off the black which forms upon the edges, and to drive down the

carbonized tar which attaches itself to the upper part of the jets.

BLEACHING (_Blanchiment_, Fr.; _Bleichen_, Germ.) is the process by

which the textile filaments, cotton, flax, hemp, wool, silk, and the

cloths made of them, as well as various vegetable and animal substances,

are deprived of their natural colour, and rendered nearly or altogether

white. The term bleaching comes from the French verb _blanchir_, to

whiten. The word _blanch_, which has the same origin, is applied to the

whitening of living plants by making them grow in the dark, as when the

stems of celery are covered over with mould.

The operations which the bleacher has recourse to differ according to

the nature of the bleaching means, the property of the stuff to be

bleached, and local customs or circumstances; and the result is also

obtained with more or less rapidity, certainty, economy, and perfection.

The destruction of the colouring matters attached to the bodies to be

bleached is effected either by the action of the air and light, of

chlorine, or sulphurous acid; which may be considered the three

bleaching powers employed for manufacturing purposes.

Bleaching by the influence of air and sunshine is the most ancient, and

still the most common, method in several civilised countries; it is also

supposed by many to be the least injurious to the texture of yarn and

cloth. The operations it involves are very simple, consisting in the

exposure of the goods upon a grass-plat to the sky, with their

occasional aspersion with moisture if necessary, in addition to the rain

and dew. The atmospheric air effects the bleaching by means of its

oxygenous constituent, which combines with the colouring matter, or its

elements carbon and hydrogen, and either makes it nearly white, or

converts it into a substance easily soluble in water and alkaline

solutions. This natural process is too slow to suit the modern demands

of the cotton and linen manufacturers. Fortunately for them, a new

bleaching agent, unknown to our forefathers, has been discovered in

chlorine, formerly called oxymuriatic acid, an agent modified by

chemistry so as to give an astonishing degree of rapidity, economy, and

perfection, to this important art. It is, however, not a little

surprising, that the science which has so greatly advanced its practical

part should have left its theory far from complete, and should afford no

satisfactory answers to the two following questions.--What is the action

of the solar rays upon the colouring matter? How do air and chlorine

operate upon this principle? Some suppose that light _predisposes_ the

colouring matter to combine with oxygen; others fancy that it acts

merely in the manner of a high temperature, so as to determine a

reaction between the elements of that substance, and to cause a new

combination possessed of peculiar properties. It is generally admitted

at the present day, that a portion of the oxygen of the air passes into

the colouring matter, and changes its constitution. This is, however,

probably not the part which oxygen plays, nor is it the only principle

in the atmosphere which exercises a bleaching influence. Neither is the

action of chlorine such as has been commonly represented in our chemical

systems.

But if authors offer us only vague hypotheses concerning the three

principal agents, light, oxygen, chlorine, they afford no information

whatever concerning the phenomena due to greasy spots so frequently

found upon cotton cloth, and so very troublesome to the bleacher. It has

indeed been sometimes said in bleach-works, that fatty substances are no

longer soluble in alkalies when they are combined with oxygen. The very

reverse of this statement is probably nearer the truth.

The object of bleaching is to separate from the textile fibre, by

suitable operations, all the substances which mask its intrinsic

whiteness; or which, in the course of ulterior dyeing operations, may

produce injurious effects. In this latter respect, cotton deserves

especial consideration. This substance is covered with a resinous

matter, which obstructs its absorption of moisture, and with a yellow

colouring matter in very small quantity, often so inconsiderable in some

cottons, that it would be unnecessary to bleach them, before submitting

them to the dyer, were it not that the manipulations which they undergo

introduce certain impurities which are more or less injurious, and must

be removed. It is in fact a circumstance well known in the factories,

that unbleached cottons may be dyed any dark colour, provided they are

deprived of that matter which makes them difficult to moisten. The

substances present in cotton goods are the following:--

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