BLEACHING. 445 | 
drogen; either of these yields up its oxygen to 
the colour until all the chlorine is changed into 
muriatic acid. Others believe that the chlorine 
combines directly with the hydrogen of the cclour 
to muriatic acid; while some think it is substi- 
tuted for the hydrogen. In any case, whether 
by oxidation, dehydrogenation, or substitution, 
the colour is destroyed. But from the powerful 
action of chlorine, even when dilute, it cannot 
be continued for a long time, as it would destroy 
the fibre, as well as the colour. Hence it is well 
adapted to cotton, whose colour is easily re- 
moved, but it can only be employed as an assist- 
ant in linen bleaching, whose colour more stub- 
bornly resists decomposition. Warmth assists 
the action of chlorine, but is apt to be injurious 
to the fibre. A little dilute sulphuric acid may 
be added to the chloride of lime when largely 
diluted with water, and is thought to hasten its 
action, from the formation of chlorite of lime or 
oxygenated water, which remain in the bath 
when dilute and cold. For it has been found 
that even when a sufficient quantity of acid is 
added to decompose nearly all the bleaching salt, 
in a dilute and cold bath, its bleaching power is 
undiminished or imperceptibly weakened after 
the lapse of some days. 
Linen—Chlorine and souring, with sulphuric 
acid, have been latterly employed as an aid to 
the bleaching process of linen, and it would seem 
without injury to the fibre, which loses even less 
in weight than by the older process. The first 
steps are usually the same to about the 5th buck- 
ing, as shown in the following view of the process. 
1, 2. Steeping in weak, warm lye. 
3 to 7. Bucking, exposure, and washing. 
8. Souring 12 hours in dilute acid, and washing. 
9, 10. Steeping, bucking, &c. 
. Chemicking (chloride of lime), washing. 
. Souring and washing. 
. Bucking and exposure. 
. Chemicking and washing. 
. Souring and washing. 
. Bucking and exposure. 
. Souring and washing. 
. Washed with soap, and thoroughly with water. 
The chemic or bath of chloride of lime is some- 
times employed but once, sometimes three times. 
Chloride of soda or potassa is frequently employed 
instead of lime. The linen is washed after being 
in the chlorine-bath, and previous to souring, for 
immediate souring after the bleaching salt weak- 
ens the fibre. The action is similar to that above, 
with this difference, that the chlorine is developed 
more slowly. By the assistance of chlorine the 
time of bleaching linen is shortened some 3 to 5 
weeks. 
Rags.—The sorted, cut, and dusted rags are 
thrown into a tight vat, in which they are boiled 
with milk of lime containing a little alkali to re- 
move grease, loosen colours, &c., or interstratified 
with dry lime and a little alkali, are steamed. 
They are then washed in the engine and reduced 
to half-stuff, when the chloride of lime is thrown 
in and worked through the mass by the engine, 
the gates being closed. Dilute oil of vitriol is 
then let on the mixture and worked through in 
order to develop chlorine; after which the gates 
are opened, and, while reducing to fine pulp, the 
current of water removes the salts of lime. A 
solution strong enough to bleach dark-coloured 
rags must weaken the fibre, to avoid which a 
second bath of chloride may be resorted to; by 
washing off the salts from the first, then passing 
a little alkali through, and adding chloride afresh, 
or immediately adding the latter after washing, 
and then souring and washing as before. When 
chloride is applied in two portions, a small quan- 
tity is used with less injury to the fibre. Muri- 
atic acid may be substituted advantageously for 
sulphuric, from the greater solubility of chlorides 
over sulphates. To prevent paper from becom- 
ing yellow, after bleaching and washing off the 
salts of lime, work a little alkali through the 
engine, with the gates down, and wash off the 
residue with water. The principles are the same 
as explained above under the bleaching of cotton 
by chlorine. 
IIL. 
The vapour of burning sulphur is employed for 
removing colour from, or whitening wool, silk, 
and straw. 
Wool.—Neither chlorine nor atmospheric bleach- 
ing can be employed for wool, as they rather ren- 
der it dirty yellow. Wool containsa greasy coat- 
ing, called the yolk, arising from the sweat of 
sheep, which is composed of a potash soap, toge- 
ther with acetate, carbonate, and muriate of po- 
tassa, a salt of lime, and an animal substance, the 
cause of its peculiar odour. The greater part of 
the yolk is soluble in water, but alkali removes it 
more perfectly. Itis usual to employ putrid hu- 
man urine, diluted with 4 to 8 times as much 
water, warmed to 100° or a little more, into which 
the wool is steeped for a short time, taken out, 
drained, and washed. The yolk may also be re- 
moved by weak and warm soap-water, or a little 
very dilute carbonated or caustic potassa or soda, 
or both soap and a little alkali; but the use of 
alkali requires more care, lest the fibre should be 
attacked, and hence it is only used, if at all, for 
inferior kinds of wool. A continuance in the 
urine or alkali, and too high a temperature, injure 
woollen fibre. The loose wool should not be 
worked about too much, which would cause it to 
felt, and thereby injure it for spinning. 
After washing, the bleaching is performed by 
exposing the moistened wool in a close chamber 
to the vapour of burning sulphur, or it is steeped 
in water acidulated by sulphurous acid. The 
latter solution is made by passing sulphurous 
acid gas, derived from oil of vitriol and charcoal, 
into water. See Sunpuur. Sulphuring by the 
gas of burning sulphur is more commonly prac- 
tised, and is more economical, but the liquid 
acid, while it bleaches equally well, renders the 
wool less harsh and crisp, and does not injure 
SuLtepHuRovuS BLEACHING. 
