BLEACHING. 
calcareous earth may not mfx itfelf with the linen, as its 
particles might corrode or wear it by their hardnefs. By 
this management the lixivium being rendered more ac¬ 
tive, does not require fo large a quantity of alkali ; and 
neverthelefs, if the quantity of alkali be not too confider- 
able, it produces no damage to the cloth, notwithllanding 
the contrary prejudice, which is very general. He has 
likevvile remarked, that it was of no advantage, and even 
prejudicial, that the lixiviations fliould be of long dura¬ 
tion ; but it is neceflary that the fluid be very hot, and 
of confiderable ftrength, othervvife the cloths bleached 
by the aerated marine acid would become coloured and 
ruddy when fubmitted to new lixiviations. This accident 
took place in the trials already mentioned. Cottons are 
much more eafily and fpeedily bleached than linens : two 
lixiviums, or at molt three, with the fame number of im- 
merlions in the liquid, are fufficient; and, as they are fo 
much the more readily bleached, it is advantageous, when 
linen, hemp, and cotton, are to be bleached, to referve 
the liquors for the latter, which have been already weak¬ 
ened by exerting their aftion on the former. Such liquors 
as are fo exhaufted as fcarcely to aft upon hemp or linen, 
will do very well for cotton. After the laft immerlion in 
the liquor, the cloth mu ft be plunged in four milk, or 
water acidulated with vitriolic acid. The true proportion 
is not well afcertained ; but M. Berthollet thinks, from 
his experiments, that one part of the acid by weight, with 
fifty parts of water, may be employed fuccefsfully, and 
without danger. The cloths are to be kept about half an 
hour in this fluid, warmed ; after which, they mud be 
ftrongly, prefled, or wrung, and immediately plunged in 
common water : for, if they were fuffered to dry by eva¬ 
poration, the vitriolic acid, becoming concentrated, would 
attack them. When the cloths are well walked, nothing 
more is neceflary than to dry and prepare them in the 
ufual manner. It is an obvious precaution, that this acid 
water be not too ftrong, as it would, of courfe, injure the 
texture of the fluff's. 
The annexed plate exhibits the above-mentioned appa¬ 
ratus for preparing the oxygenated muriatic acid, which 
is ufed in this new method of bleaching. A B C D, is 
a reverberatory furnace, having, on a line with B, many 
fmall openings in its ci^umference, to ferve as chimneys ; 
within which, upon a land-bath a, is placed a mattrafs or 
diftillatory veil'd b, the neck of which Hands up above 
the furnace, running through the opening D, which is to 
be doled with clay. The mouth F, of the neck of the 
mattrafs, is clofed by a cork G, through the middle of 
which paffes a tube H, which forms a communication be¬ 
tween the infide of the mattrafs b, and the intermediate 
veffel K, where it alfo paffes through a cork I, which 
clofes one of the three openings of that veffel. The 
corks G and I ought to be prepared before-hand, and well 
fitted to each end of the tube of communication H, which 
is to be fo difpofed that it may be fitted in immediately 
after the mixture is made in the diftillatory veffel. The 
intermediate veil'd K muff be about an eighth part full of 
water ; and into it is plunged the tube of fafety L, to pre¬ 
vent danger from regurgitation. This tube ought to be 
fo high, that the weight of water which enters into it, by 
the prdTure of the gas, may be great enough to catife the 
gas to pafs into the pneumatic tub or cafk N O P, by the 
tube of communication M, which is plunged therein, 
and reaches to the bottom, where it is bent horizontally, 
fo that the gas may be emitted under the firft of the three 
wooden, or (if they can be procured) ffone-ware, cavi¬ 
ties, or receivers, which are placed in the infide of the 
tub, one above the other. O is a handle, which ferves to 
turn the agitator E, the movement of which facilitates 
the combination of the gas with the water. P is a fpigot 
and faucet to draw off the liquor. 
Fig. 2. represents the upper part of the pneumatic 
calk ; in which Qjl S T are four Haves whicli are thicker 
than the others, and whicli projeft within the tub, when 
they are hollowed fo as to receive the ends of two wooden 
99 
bars U V, which ferve to keep in their places the cavities 
or receivers X Z. The tube M (hews where the oxyge¬ 
nated muriatic gas enters from the diftillatory veffel, and 
P (hews where it is drawn off for ufe. 
Fig. 3. is a longitudinal fection of the cafk. Each ca- 
vity X is fo conffrufted that it may receive the gas, which 
is emitted at i from the tube of communication M. The 
gas, as it comes out, is collefted under the lowed cavity, 
and increafes in quantity until it paffes by the funnel Z 
to that in the middle, and afterwards to the upper one. 
The opening through which the agitator E paffes, in the 
centre of each cavity, is in the fhape of a funnel, and is 
fo formed as to hinder the gas from efcaping along the 
agitator, which is furniflied with three tranfverfe arms 
ccc, each being faftened by a wedge ddd\ ef at fig. 4. 
reprefents one of thefe arms in a horizontal direftion. 
The bent tube gh ferves to draw oft’ the atmofpheric air 
which is contained under the cavities, after the cafk lias 
been filled with water. To make ufe of this tube, the 
bent part is fucceffively introduced under each cavity, as 
is (hewn at g •, it muff be blown into at the end h, till the 
water in it is forced out : after which the air contained 
under the cavity will immediately make its efcape. 
Fig. 5. reprefents the apparatus for the diffillation of 
common muriatic acid ; in which l reprefents a retort, 
which is to be placed in a reverbatory furnace, as before ; 
the mouth of the retort is to be clofed by a cork m, having 
two holes, through one of which paffes the tube n, bent 
at 0, and terminating at the top in the form of a funnel p, 
by means of which the vitriolic acid is to be introduced 
into the retort. The only hole of the cork m receives the 
end of a tube q, whicli forms a communication between 
the retort and a veffel r ; which veffel has three openings, 
and is to be about an eighth part full of water, into which 
is alfo to be plunged the tube of fafety s, to prevent dan¬ 
ger from regurgitation : the veffel r has a communication' 
with a fecond veffel u, by means of the tube t : this fecond 
veffel is to be half full of water, and is to have a com¬ 
munication with a third : this third vellol fliould be alfo 
provided with a tube of fafety, and is to communicate 
with a fourth. 
M. de Croifille makes ufe of a folution of indigo in the 
vitriolic acid; for which purpofe he takes one part of 
finely-pulverized indigo, with eight parts of concentrated- 
vitriolic acid. This mixture is kept in a mattrafs for fe- 
veral hours on the water-bath ; and, when the folution is 
complete, it is diluted with a thoufand parts of water. 
In order to afeertain the force of the oxygenated muriatic 
acid, one meafure of this folution is put into a graduated 
tube of glafs, and the liquor or impregnated water is 
added, until the colour of the indigo is completely de- 
ftroyed. In this way it is afcertained, by means of the 
graduations, how many meafures of any liquor, whofe 
goodnefs has been afcertained by direft experiments upon 
linen or cotton, are neceflary to deftroy the colour of one 
meafure of the folution of indigo ; and this number wilL 
ferve to afeertain the refpeftive force of all the liquors 
which are required to be compared together. Mr. Watt 
makes ufe of a,folution of cochineal for the fame purpofe. 
M. Berthollet lias fince publifhed forne additions to the 
foregoing Memoir, which are as follow:—“ Mr. Welter 
finds that it is advantageous to terminate the procefs by 
expofing the thread or doth for three or four days in the 
field ; during which they muff be occafionally watered, 
and afterwards wafhed with pure water.” He conliders 
this expofition as indifpenfable. But M. Berthollet ob- 
ferves, that other perlons have bleached, to the perfeft 
fatisfaftion of artifts, without it; though he admits that 
it may happen, in the large way, that certain pieces may 
not turn out’perfeftly white after the laft operation, in 
confequence of fome of their parts having fuffered cafual 
p re flu re ; and he thinks that, although a continuance of 
the operation would remove thefe imperfeftions, it might, 
in fucb cafes, prove more advantageous to remove them 
by expofure on the grafs 5 very little lofs of time, and no 
3 confidetabls 
