BLEACHING. 
allowed to subside, and the clear liquor was 
fit for the purpose of bleaching. 
An improvement, however, of still more 
importance has been made by Mr. Tennant 
of Glasgow, and a patent obtained for it ; 
viz. that of combining the oxymuriatic acid 
with dry lime, and dissolving a certain pro- 
portion of this compound in water to form a 
bleaching iiquor. It perhaps could scarcely 
have been supposed that such a combina- 
tion could have been formed, so as to retain 
the powers of the acid. But the trial has 
fully succeeded, and the advantages derived 
from it are important ; the compound can 
be carried easily to a distance, and the ma- 
nufacturer need not prepare it himself, which 
is always an advantage, especially where he 
does not work on a large scale. The com- 
bination is formed by introducing the oxy- 
mnriatic acid gas through leaden tubes into 
slaked lime, prepared from chalk, by which 
it is absorbed. Solutions of this are pre- 
pared of different strengths,, according to the 
purposes to which they are to be applied, 
the strength being judged of by the hydro- 
meter, aDd by the quantity requisite to de- 
stroy the colour of a diluted solution of in- 
digo in sulphuric acid. The process of 
bleaching, as now performed by these li- 
quors, differs little from that which has been 
already described as executed by the solu- 
tion of the oxymuriatic acid alone in water. 
To these methods, however, is to be added 
the more, recent discovery of bleaching by 
an alkali, assisted by watery vapour and a 
high temperature, and which, either alone 
or combined to a certain extent with the 
method by the oxymuriatic acid, is now 
practised with so much advantage. In this 
method, which has been long in use in some 
of the eastern countries, and of which notice 
was first given by Chaptal, the cloth or 
thread is impregnated . with a solution of 
potash or soda, rendered active by the car- 
bonic acid having been entirely abstracted 
from the alkali by lime; it is suspended 
loosely, and, with an extensive surface, in a 
close boiler, a quantity of the same solution 
being in the bottom, and heat is applied, 
the boiler being closed, with a safety valve 
in the cover, so t? *t the vapour under pres- 
sure may receive a high temperature. It 
is kept in this situation for a number of 
hours. The thread or cloth when cold is 
washed, and either exposed on the field, or 
subjected to the action of the oxymuriatic 
acid in some of the forms under which it 
has been used. It is thus at once rendered 
perfectly white. The superiority of this 
method probably arises from the high tent 
perature, and the solvent power of the wa- 
tery vapour, favouring the action of tha 
alkali on the colouring matter, while this 
vapour penetrates (he fibres of the cloth so 
effectually, that tire matter is in a great 
measure dissolved and removed. 
The aniii'ia! fibres that are subjected to 
the bleaching process are wool and silk. 
These cannot be treated in the same manner 
as vegetable substances : a strong alkaline 
ley will dissolve them, and oxymuriatic acid 
will both weaken them and turn them yel- 
low. The colour of manufactured wool re- 
sides partly in its own oil, and partly in the 
greasy and mucilaginous applications which 
it receives in being prepared for the loom. 
Both the one and the other are easily got 
rid of, by the action of fuller’s earth and 
soap in the process of fulling. Fuller’s 
earth is a very fine-grained absorbent earth, 
which by itself is capable of mixing rather 
than combining with vegetable or animal 
oils, and rendering them miscible with wa- 
ter : its action is found, however, to be in- 
creased by the addition of soap and woollen 
cloth being beat in a fulling-mill with hot 
water, and a proper mixture of earth and 
soap, or of soap alone, and afterwards well 
washed and dried in the air, receives all the 
bleaching which it requires, or is indeed 
capable of. It is then of a white colour, 
somewhat verging towards yellow: this last 
tinge may be made to disappear by the ad- 
dition of a very smail quantity of stone blue 
in the water in which the cloth is last wash- 
ed, or by exposing it to the fumes of burn- 
ing sulphur. By this latter method, how- 
ever, it acquires a certain harshness of feel, 
and is apt to turn very yellow when washed 
with soap. Both the colour and harshness 
of raw silk depend entirely on a yellow var- 
nish with which it is naturally covered. 
This varnish may be in part removed by 
long boiling in simple water. It is consi- 
derably more soluble in alcohol; but the 
most effectual and expeditious way of clear- 
ing is by putting it in a linen bag, and boil- 
ing it for some hours in a solution of white 
soap in water, then rincing it in clean wa- 
ter, and repeating the process till it is quite 
white, and exhibits the peculiar lustre of 
this beautiful substance. Some of the 
French chemists have endeavoured to lessen 
the consumption of soap, by proposing va- 
rious substitutes ; but nothing is so effectual 
and expeditious as the purest white soap, 
and the article itself is so valuable, as amply 
to repay this expense. 
N 11 % 
