98 B L E A C 
dried after this wafhing. M. Berthollet is of opinion, 
from this, that, when the calx of manganefe contains much 
phlogifticated air, it is fcarcely proper to form the oxyge¬ 
nated muriatic acid : M. Fourcroy however afferts, that 
the phlogifticated air efcapes in diftillation from manga¬ 
nefe by a degree of heat lefs than ignition, but that igni¬ 
tion is neceffary to deprive it of its vital air. It might per¬ 
haps be found advantageous to make ufe of this informa¬ 
tion to purify Inch manganefe as contains phlogifticated 
air, by diddling off this lad aerial fubftance by a mode¬ 
rate heat before it is applied to the purpofe of oxygenating 
the marine acid. 
A greater or lefs quantity of water mud be added, not 
only according to the degree of the concentration of the 
lulphuric acid, but likewife according to the quantity of 
matter fubjedted to didillation. If this quantity be con- 
liderable, the acid mud be more diluted than if it be frnall. 
It might be more advantageous to make ufe of an acid 
which had not been concentrated ; becaufe the operation 
of concentrating it adds to its price, and it is obliged to 
be again diluted with water. But M. Berthollet obferves, 
that this faving can only take place when the manufactory 
of the vitriolic acid is near at hand ; for, in thofe fituations 
where this acid is to be brought from a condderable dif- 
tance, the expence of carriage of a greater quantity of 
fluid might exceed that of concentrating it. When the 
materials are prepared, the calx of manganefe mud be 
carefully mixed with the fea-falt, and the mixture intro¬ 
duced into the didillatory veffel, placed on a fand bath : 
the vitriolic acid mud then be diluted, and differed to 
cool; after which it is to be poured on the mixture, and 
the tube of communication between the mattrafs and the 
intermediate veffel quickly fitted in. A particular atten¬ 
tion to the lutings is required in this operation. M. Chap- 
tal takes notice, that, when the vapour is perceived to ef- 
cape by the fmell, it is fometimes difficult to afcertain the 
imperfeCt place ; but that, if a feather dipped in volatile 
alkali be paffied on fiich occafions over the lutes, it will 
lhew the faulty place, by the white cloud of ammoniac 
formed in confequence of the combination of the marine 
acid with the volatile alkali. The fize of the veffels ought 
to be fuch, that the mattrafs ffiould be about one-third 
empty ; and that, for the quantity here laid down, the 
calks ihould contain one hundred pints of water, with 
an empty fpace of the bulk of about ten pints ; becaufe, 
when the gas comes to occupy the cavities defigned to re¬ 
ceive it, the water will require a fpace into which it may 
afcend. 
Before the operation is begun, the pneumatic calk mud 
be filled. The mixture being made, the gas, which foon 
begins to be difengaged, firft drives the atmofpheric air 
out of the apparatus. As foon as it is apprehened that 
the atmofpheric air has palled into the cavities, it is emp¬ 
tied out by the means of a recurved tube, which is 
fucceffively introduced beneath each. The operation 
is now differed to go on without the application of heat, 
until it is perceived that the bubbles are more flovvly emit¬ 
ted : at this period, a flight degree of heat is applied. It 
mud not be ftrongly urged at the beginning; but by a gra¬ 
dual increafe it is at lad to be carried to ebullition, to¬ 
wards the end of the operation. It may be known when 
the operation is near its termination, by the tube of com¬ 
munication and intermediate veffel becoming hot. When 
the gas is no longer difengaged but in frnall quantities, the 
lire is to be put out, and a diffident time mud be differed 
to elapfe until the mattrafs is nearly cold. The tube of 
communication may then be removed, and hot water 
poured in to keep the matter in folution, that it may be 
more eafily taken out : this refidue is to be poured into a 
large veffel intended to preferve it for ufe. The opera¬ 
tion lads longer in proportion to the quantity of matter. 
With the before-mentioned quantity, it ought to lad dve 
or fix hours. It is proper not to be too much in hade, 
becaufe a larger quantity of gas is by that means obtained. 
H I N G. 
One fingle perfon may infped: and manage feveral of thefe 
didillations, and the quantities may be much larger. 
The intermediate veffel gradually becomes filled with a 
fluid, which confids of pure but weak muriatic acid : fe¬ 
veral operations may however be made without taking it 
out ; but, when it is apprehended that there is not a fuffi- 
cient fpace left empty, this acid is taken out by means of 
a fyphon : and, when its quantity is confiderable enough, 
it may be fnbdituted indead of the mixture of fulphuric 
acid and muriate of foda, in a fimilar operation, if it be 
not wanted for another ufe. In order that the quantity of 
common muriatic acid which pafles out of the mattrafs 
may be inconfiderable, it is expedient that the fird tube 
Ihould make a right angle, or even a more obtufe angle, 
with the body of the mattrafs. During the operation, it 
is neceffary to dir the water, from time to time, by means 
of the agitator, in the apparatus, to favour the ablorp- 
lion of the gas by the water. When this is completed, 
the liquor is diffidently flrong to be ufed in bleaching. A 
fmaller proportion of water may be put into the calk, and 
the fluid may afterwards be properly diluted. In this 
date of concentration, though the liquor retains a con- 
liderably drong fmell, yet it cannot prove noxious, or even 
very inconvenient, to thofe who ufe it. It is, neverthe- 
lefs, proper to conduct it into the vedels in which the 
cloths are arranged by wooden channels, fitted to the open¬ 
ing at the lower part of the calk. It is proper to draw off 
the liquor from the cafk as foon as it is prepared, becaufe 
it a£ts upon the wood, and not only becomes, by that 
means, weaker, but likewife hadens the deftruftion of the 
calk : but, when it is conveyed into a veffel in which cloths 
are properly placed, thefe fpeedily weaken it to fuch a 
degree, that it does not perceptibly a£t upon the wood. 
The clothsare to be prepared by leaving them twenty-four 
hours in water, or dill better in the old lixivium, to ex- 
tradl the dreffing ; after which they mud be once or twice 
well wadied in alkaline lixiviums, becaufe all that part 
which can be extradded by the lixiviums would have neu¬ 
tralized a portion of the liquor, which requires to be care¬ 
fully ufed. After this the cloth mud be carefully wafhed, 
and difpofed upon dicks in fuch a manner that it may be 
impregnated with the liquor poured on it, without any 
part being compreffed. The framing of the dicks, as 
well as the cafk and veffel intended to contain the cloths, 
ought to be conftrudted without iron ; becaufe this metal 
becomes calcined by the oxygenated muriatic acid, and 
would produce iron-moulds, s&t to be taken out but by 
means of fait of forrel. The fird immerfion mud be longer 
than the following ones; it may lad three hours: after 
which, the cloth is to be taken out, lixiviated anew, and 
then put into a fliallow veffel, in order that new liquor 
may be poured upon it. It is fufficient that this immer¬ 
fion, and the following, Ihould continue for the fpace of 
half an hour. The cloth is taken out, and cleared of the 
liquor by preffure ; then lixiviated, and fubjeded to new 
immerfions. The fame liquor may be ufed until it is ex- 
haufted ; and when it is found to be much weakened, a 
proportion of the liquor which has not been ufed may be 
added. When the cloth appears white, excepting at the 
felvages, and a few threads darker than the reft, it muft 
be impregnated with black foap, and ftrongly rubbed ; 
after which it is to be lixiviated for the laft time, and im- 
merfed once more in the liquor. 
The number of lixiviations and immerfions which are 
neceffary, cannot be determined, becaufe it varies accord¬ 
ing to the nature of the cloth the limits of this number, 
however, are between four and eight, for linen and hempen 
cloths. M. Berthollet expreffes his inability to point out 
the beft method of making the alkaline lixiviums; this 
ufeful art being ftill a matter of mere practice, and vari- 
oully performed in different places. It appeared advan¬ 
tageous to him to render the alkali cauftic, by mixing one 
third of lime ; but in this cafe care muft be taken that the 
lixivium be drained through a cloth, in order that the 
calcareous 
