228 
sure of vegetable matters on the grass, sub - 
jects them to the action of the solar rays; 
and moistening them during their exposure, 
ia dilates, with the evaporation of the water, 
the emanation of the carbonic acid formed by 
the oxygen of tire atmosphere, which com- 
bines with the carbon resulting from the al- 
kaline combustion. It even agrees pretty 
well with theory, in terminating the process 
■of bleaching, to immerse the cloth and thread 
iii sour milk, acidulous liquors, or, what is 
more convenient, very weak sulphuric acid. 
In proportion as the alkali, during the 
first immersion, destroys the colouring mat- 
ter, the oxygen of the atmosphere, or that 
furnished by the oxygenated -muriatic acid, j 
joins that carbonized matter, and forms car- j 
bonic acid, which afterwards resolves itself j 
into gas. This is contained the more in the 
principles, as the bases of all the acids are ; 
insoluble in water; but when the combi na- j 
tion takes place between the carbon and the 
Oxygen, it immediately becomes soluble. 
Thus, on tiie one hand to burn the colouring 
matter, and to dissolve it on the other, form 
the whole secret of the art of bleaching ; and | 
the greater or less tendency of vegetable sub- j 
stances to experience that combustion, con- j 
stitutes the gradations of their whiteness, and | 
the facility or difficulty of bleaching. 
The slowness of the whole process arose, I 
in a great measure, from bleachers being un- , 
acquainted witii these principles. A long 
succession of levs, and exposure on the grass, 
was necessary to penetrate- the fibres of the 
linen from stratum to stratum. The texture 
was sufficiently close to resist the action of 
the heat of a common ley, and a considerable 
time was required to -absorb the oxygen pre- 
sented by the delicate stratum of atmospheric 
air. , j 
In the process of bleaching by steam, these 
difficulties are removed. The high tempe- , 
rature of the steam, in the interior part of the 
apparatus, swells up the fibres of the thread 
or cloth ; the pure alkali, which rises with 
the elastic fluid, seizes with avidity on the i 
colouring matter, and burns it ; seldom does j 
the tissue of the flax or hemp resist the pene- 
trating effect of this vapour-bath. The whole 
matter, therefore, by which they are colour- 
ed, is attacked and decomposed by this single 
operation ; and even if we suppose that a part 
has been able to resist, nothing is necessary 
but to repeat tlie operation, alter a previous 
immersion and exposure on the grass, to en- 
sure its complete effect. The alkali even ap- 
pears to have a much livelier and more caustic 
action, when it is combined with caloric, than 
in ordinary leys, where the temperature never 
rises above 162° of Fahrenheit. By making 
the cloth or thread pass through one ley of 
oxygenated muriatic acid, or oxygenated 
muriate of lime, an union is effected between 
the solution and the carbon, arising from the 
burning of the extracto-mucous matter of tire 
(lax; carbonic acid is formed; the water 
even in which this new compound is diluted, 
concurs to promote this combination ; if the 
doth is then exposed on the grass, the car- 
bonic acid is dissipated, and the cloth is 
bleached. 
It was believed thattlie steam of a pure al- 
kaline ley would not be caustic, and would 
wot produce the same effects as the saline so- 
il' ti;m; and the reason assigned for this opi- 
nion was the concentration of all the salts by 
BLEACHING. 
the evaporation of the aqueous fluid : but 
what takes place in the open air, where the 
atmosphere every moment absorbs the mois- 
ture which is evaporated, cannot be applied 
to a close apparatus, where the temperature 
is elevated in an extreme degree ; besides, 
the calorie always carries with it a little al- 
kali, even in low temperatures, as is observed 
when water is poured over potash ; the steam 
which issues from it changes blue vegetable 
colours to green. 
Jt follows, from these chemical principles, 
that the* action of steam alone does not 
bleach, and that the concurrence of oxygen 
is necessary to aid the composition of the car- 
bonic acid ; this acid requires for its for- 
mation, 28 parts of carbon, saturated with 
72 of oxygen : but all the oxygen contained 
in the apparatus would not be sufficient to 
saturate the considerable quantity of colour- 
ing matter burnt by the alkaline combustion, 
and converted into carbon ; this deficit must 
be supplied by immersion in any oxyge- 
nated liquor whatever, and the dispersion of 
the elastic fluid thus formed must be then 
facilitated by exposure on the grass. 
To bleach doth in tins manner, it must be 
immersed in a slight alkaline caustic liquor, 
and placed in a chamber constructed over 
a boiler, into which is put the alkaline ley 
which is to be raised into steam. After the 
fire has been lighted, and the cloth has re- 
mained exposed to the action of the steam 
for a sufficient length of time, it is taken out, 
and immersed in the oxygenated muriate of 
lime, and afterwards exposed for two or 
three days on the grass. This operation, 
which is very expeditious, will be sufficient 
for cotton ; but if linen cloth should still re- 
tain a yellow tint, a second alkaline caustic 
vapour-bath, and two or three days on the 
grass, will be sufficient to give it the neces- 
tary degree of whiteness. 
| Bleaching of cotton. Cotton is a fila- 
mentous substance, or a kind of down which 
envelopes the seeds of the cotton-plant. 
r J his plant or shrub comes originally from the 
| East, and grows only in warm climates. 
This substance, after being separated from 
! the seeds, is always charged with a coarse 
colouring matter, which soils it, and renders 
it opaque. The presence of this unctuous 
matter is proved by the slowness with which 
cotton absorbs water before it is scoured, and 
by the force with which it absorbs it after the 
operation ; by which means, from being 
opaque, it is rendered clear and transparent. 
Cotton varies a great deal in its qualities, 
according to the different kinds, the climate 
where produced, and the culture employed. 
Its colour is sometimes yellow, and sometimes 
white ; but in general it is of a dirty yel- 
low. 
To bleach it, does not require the same 
prepa.ations as hemp and flax. The first 
operation consists in scouring it in a slight 
alkaline solution, or, what is better, by ex- 
posure to steam. It is afterwards put into 
! a basket, and rinsed in running water. The 
! immersing of cotton in an alkaline ley, how- 
j ever it may be rinsed, always leaves with it 
| an earthy deposit. It is well known that 
j cotton bears the action of acids better than 
hemp or flax; that time is even necessary 
before the action of them can be prejudicial 
to it : and by taking advantage of this valu- 
able property in regard to bleaching, means 
have been found to free it from the earthy 
deposit, by pressing down the cotton in a 
very weak solution of sulphuric acid, and 
afterwards removing the acid by washing, 
lest too long remaining in it should destroy 
the cotton. 
Bleaching of xvool. 1 he substances pro- 
duced by the animal kingdom, differ essen- 
tially in their constituent principles from ve- 
getables. Vegetables serve as the nourisiv- 
lnent to the animals and insects, the spoils 
of which we employ. Animalized by their 
organs, they acquire oilier properties. We 
shall here confine ourselves to the examina- 
tion of wool and silk, as the animal substance* 
most generally employed for clothing. 
Wool js a liner kind of hair with which the 
bodies of several animals are covered. It is 
composed of filaments or tubes, filled with 
an oily or medullary substance. The sides 
of these tubes are perforated with a multi- 
tude of small pores, which communicate with 
a longitudinal tube. By chemical analysis 
wool gives a great deal of oil, and carbonate 
of ammonia; caustic alkaline leys dissolve it 
entirely. It experiences no change in boil- 
ing water ; it alters ven little when preserv- 
ed in a place well aired ; acids have very 
little action on it ; when exposed to a strong 
heat, it enters into fusion. 
An examination of these chemical facts, is 
necessary for understanding the principles 
which ought to direct the artist in the bleach- 
ing of this substance. The little action which 
acids have upon wool, and its unalterableness 
in water even when aided by heat, render it 
necessary to have recourse to alkaline or 
saponaceous leys; but its solubility in these 
salts shews, that great prudence and caution 
must be employed. In regard to acids, none 
have been hitherto used but the sulphureous 
acid, obtained in the gaseous state by com- 
bustion. 
In the preliminary operations to which 
wool is subjected, it is customary to leave a 
little of its grease, to secure it from insects. 
Wool is often freed from the grease by the 
farmers, when they wish to sell it' at a high, 
price; but in the subsequent manipulations, 
it is greased or oiled before it is combed, spun, 
&c.; and as this fat matter attracts dust, it 
dirties and thickens the stuffs. The first kind 
of bleaching to which wool is subjected, is to 
free it from these impurities. This operation 
is called scouring. In manufactories, it is 
generally performed by means of an ammo- 
niacal ley, formed of five measures of river 
y, after and one of stale urine ; the wool is 
immersed for about twenty minutes in a bath 
of this mixture, heated to fifty-six degrees; 
it is then taken out, suffered to drain, and then 
rinsed in running water: this manipulation 
softens the wool, and gives it the first degree 
of whiteness : it is repeated a second, and 
even a third time, after which the wool is fit. 
to be employed. In some places, scouring 
is performed with water slightly impregnated: 
with soap ; and indeed, for valuable articles, 
this process is preferable, but it is too expen- 
sive for articles of less value. 
k ulling the cloth adds still to the whiteness, 
and if an increased degree is necessary, it 
may be procured by the action of the sul- 
phureous acid ; that is to say, of the fumes 
of sulphur in a state of combustion, or the 
vapour of that acid condensed and combined 
with water. 
