BLEACHING. 
Salt, _ - 
60 
Sulphuric acid, 
5Q 
Water, 
50. 
The better these substances are combined 
together, the more easily will the acid gas be 
disengaged by the action of the sulphuric 
acid. 
To ascertain the strength of the acid for 
bleaching, a solution of indigo in the sulphuric 
acid is employed. The colour of this is de- 
stroyed by the oxygenated muriatic acid ; 
and according to the quantity of it tiiat can 
be discoloured by a given quantity of the 
liquor, its strength is known. 
Cloth is prepared for immersion in oxyge- 
nated water, by soaking in a ley of weak pot- 
ash, and rinsing it afterwards in a large quan- 
tity of water, in order to free it completely 
from the weaver’s dressing, and the saliva of 
the spinners. 
In this country, machinery is employed for 
rinsing and beating ; the apparatus must be 
arranged according to the objects to be 
bleached; the skeins of thread must be sus- 
pended in the tub destined for them, and the 
cloth must be rolled upon reels in the appa- 
ratus. When every thing is thus disposed, 
the tubs are filled with oxygenated muriatic 
acid, by introducing a funnel, which descends 
to the bottom of the tub, in order to prevent 
the dispersion of the gas. The cloth is 
wound, or the frame-work on which the skeins 
are suspended is turned several times, until 
it is judged,- by taking out,a small quantity 
of the liquor from time to time, and trying 
it by the test of the solution of indigo, that it 
is sufficiently exhausted. The weakened 
liquor is then drawn off, and may be again 
employed for a new saturation. 
Great difficulties for a time impeded the 
progress of this method of bleaching, arising 
chiefly from prejudice, and the ignorance of 
bleachers in chemical processes. These ob- 
stacles were, however, soon removed by Mr. 
Watt, of Glasgow, and Mr. Henry and Mr. 
Cooper at Manchester. Another difficulty 
presented itself, which had nearly proved 
fatal to the success of the operation. This 
was the want of a proper apparatus, not for 
making the acid and combining it with water, 
for this had been supplied in a very ingenious 
manner by Mr. Watt and M. Berthollet ; but 
for the purpose of immersing and bleaching 
goods in the liquor. The volatility of this 
acid, and its suffocating vapours, prevented 
its application in the way commonly used in 
dye-houses. Large cisterns were therefore 
constructed, in which pieces of stuff were 
stratified; and the liquor being poured on 
them, the cisterns were closed wiffilids. But 
this method was soon found to be defective, 
as the liquor could not be equally diffused ; 
the pieces weretberefore only partially bleach- 
ed, being white in some parts, and more or 
less coloured in others. 
Mr. Rupp, of Manchester, invented an 
apparatus for bleaching doth, exceedingly 
simple in its construction, of small expence, 
and which contains the liquor in such a man- 
ner as to prevent the escape of the oxyge- 
nated muriatic acid gas. A consideration of 
no less importance in the arrangement of 
this apparatus, is the impossibility of the va- 
pour injuring the health of the workmen. 
It was found, however, that the use of the 
oxygenated muriatic acid alone weakened' the 
cloth, and various methods of preventing its 
noxious effects upon the health of the work- 
men were -tried Without success; till it was 
discovered that an addition of alkali to the 
liquor deprived it of its suffocating effects, 
without destroying its bleaching powers. 
The process began then to be carried on in 
open vessels, and has been continued in this 
manner to the present period. The bleacher 
is now able to work his pieces in the liquor, 
and to expose every part of them to its action, 
without inconvenience. 
Potash was at first used for this purpose; 
and although this advantage was unquestion- 
ably great, it was diminished by the heavy 
expence of the potash, which was entirely 
lost. Also, the potash which was added to 
the liquor, though it did not destroy its power 
ot bleaching, diminished it; because a so- 
lution of the oxygenated muriate of potash, 
which differs from this bleaching liquor in 
nothing hut in the proportion of alkali, will 
not bleach at all. This is a well-known fact, 
from which we might infer, that the oxyge- 
nated muriatic acid will lose its power of 
destroying the colouring matter -of vegetable 
substances, in proportion as it becomes neu- 
tralized by potash. 
It was afterwards discovered that the oxy- 
muriatic acid might be combined with the 
alkaline earths, as lime and barytes, and also 
with magnesia ; by llus means forming oxy- 
muriates, which were soluble in water and 
had the property of bleaching. The oxy- 
muriate of lime is at present used in almost 
all the bleach ing-grounds. For the manner 
of prepar.ng it, Mr. Tennant took out a pa- 
tent ; but this has been lately contested, and 
it is now prepared and used by. all the bleach- 
ers through tlxe country. 
If the oxygenated muriatic acid is passed 
through iime-water, it will combine with the 
lime, and form oxymuriate of lime ; but as 
the water can only retain a small portion of 
lime, this was not found of much use. To 
cause a larger quantity of lime to combine witl: 
theoxymuriatic acid gas, the lime is mechani- 
cally suspended in the water, into which tlxe 
gas is made to pass, and agitated, so as to 
present fresh matter to the gas. By this 
means, the oxymuriate of lime is formed in 
a very convenient manner ; it is dissolved in 
water, and used as a bleaching liquor. 
T his liquor is found to be preferable to the 
oxygenated muriatic acid, and potash. At 
the great bleach-field in Ireland, four leys of 
potash are applied alternately with four w eeks 
exposure on the grass, two immersions in the 
oxygenated muriate of lime, a ley of potash 
between the two, and the exposure of a week 
on the grass between each ley and the im- 
mersions. Daring summer two leys and 
fifteen days exposure are sufficient to prepare 
cloth for the action of the oxygenated muri- 
ate ; then three alternate leys,' with, immer- 
sions in the liquor, will be sufficient to com- 
plete the bleaching: nothing then will be 
necessary, but to wind the cloth through the 
sulphuric acid. 
The oxygenated muriatic acid gas may 
also be combined with lime in a dry state, 
or the water may be evaporated, when it is 
employed for the formation of oxymuriates, 
which may then be very conveniently trans- 
ported to any distance without, injury to its 
detersive power ; an advantage not possessed 
by the acid alone, which cannot be transport- 
Ff2 
227 
ed without the loss of almost half of it 
strength. 
In all the processes for bleaching which have 
been hitherto described, we have seen that 
potash acts a distinguished part, either as an 
auxiliary, or as a principal agent. To find a 
detersive substance v Inch might be a substi- 
tute for it, was an object of the utmost im- 
portance. Mr. Kir wan suspected that it 
would be found in the sulphured of lime, and 
his opinion was confirmed by Dr. Higgins. 
Sulphur and lime are both cheap articles ; 
they are very easily combined, and this com- 
bination completely answers the purposes of 
potash, without any danger of injuring t lie 
linen. Tire suiphuret of lime is prepared in 
the following manner for the purpose of 
bleaching: Sulphur or brimstone, in fine pow- 
der, four pounds ; lime, well slaked and sift- 
ed, twenty pounds; wafer, sixteen gallons; 
these are to be well mixed, and boiled for 
about half an hour in. an iron vessel, stirring 
them briskly from time' to time. Soon after 
the agitation of boiling is over, tiie solution 
bl the suiphuret of lime clears, and may be 
drawn off free from the insoluble matter, 
which is considerable, and which rests upon 
the bottom of the boiler. T he liquor, in this 
state, is pretty nearly of the colour of small 
beer, but not quite so transparent. 
Sixteen gallons of fresh water are after- 
wards to be poured upon the insoluble dregs 
in the boiler, in order to separate the whole 
of the suiphuret from them. When this clears 
(’being previously well agitated), it is also to 
be drawn off, and mixed with the first liquor ; 
to these again thirty-three gallons more of 
water may be added, which will reduce the 
liquor to a proper standard for steeping the 
cloth. Here we have (an allowance being 
made for evaporation, and for the quantity 
retained in the dregs) sixty gallons ot iiquor 
from four pounds of brimstone. 
Although sulphur, by itself, is riot in any 
sensible degree soluble 'in water, and lime but 
sparingly so, water dissolving only about one 
seven-hundredth part of its weight of lime; 
yet the suiphuret of lime is highly soluble. 
When linen is freed from the weaver’s dress- 
ing, in the manner already described, it is to 
be steeped in the solution of suiphuret of 
lime (prepared as above) for about twelve or 
eighteen hours, then taken out and very well 
washed. When dry, it is to be steeped in the 
oxymuriate of lime for twelve or fourteen 
hours, and then washed and dried. This pro- 
cess is to be repeated six times, that is, six al- 
ternate immersions in each liquor, which has 
been found to whiten the linen. 
Steam has been lately employed with great 
success in France. The process was brought 
from the Levant. Chaptal first made it 
known to the public. 
We have already mentioned, that the 
bleaching of vegetable substances depends on 
the destruction of their colouring principle 
by tlie combined action of the air!j moisture, 
and light ; or rather, by the united influence 
of these principles to alter their natural co- 
lour. 
Alkalis have, on the colouring matter of 
vegetables, an action which produces (he 
effect of a real combustion. Were we inti- 
mately acquainted with the nature of potash 
and soda, we might be able to explain the 
cause of this burning; but it is sufficient for 
us at present to know the effect. The expo- 
