Pr-ocefsfor Bleaching Raw Silk. 89 



heat gradually applied. The firR liquor which comes over is (lightly red, turbid, and fcarcely 

 acid. This is to be thrown away, and the receivers changed. The fucceediiig produa is 

 the colourlefs marine acid, of an aromatic fmell refembling the buds of poplar. The refm 

 of the filk remains in the retort decompofed by the acid. The marine acid thus obtained 

 is weaker than it originally was ; which is in fad of little confequence, as it is pure, and 

 may be fafely ufed, either by increafing the dofe proportional to its diminiOied ftrength, or 

 by concentrating it, if required, in the ufual way. 



If this diftillation be made in a filver alembic, inftead of retorts of glafs, and a capital and 

 worm of pure tin be annexed, the alcohol will be obtained fo (lightly acid as fcarcely to 

 redden the tlndure of turnfol ; but it is fufficiently acid to receive injury if preferved in a 

 copper vefTel. 



If a cucurbit of filver be prepared, of the capacity of three or four quarts, with a glafs 

 head, the refidues of the firft diftillation may be treated in this veflel in the fame manner 

 as has been direded for glafs retorts. M. Baume affirms that he has praflifed all thefe 

 operations with glafs retorts and a fmall filver alembic, with the mod perfe£\; fuccefs ; but 

 that he made ufe of pot-adi to faturate the marine acid, becaufe he had not a filver veflel of 

 fufficient capacity. From the danger of diftilling large quantities of ardent fpirit in glafs 

 veflels, he is of opinion that no motives of economy are fufficient to juflify the rifk attend- 

 ing this method. In the ufe of tin, it is neceflary to be careful that it contains no adulte- 

 ration of lead, becaufe the vapours of marine acid have fufficient power to alter this laft 

 metal very confiderably. 



Upon the firft intimation of this new procefs in France, manufaclorles were immediately 

 eftablilhed, to the number of twenty or more, without the concurrence of Mr. Baumc, by 

 perfons who confequently were not aware of the apparently minute but very important 

 circumftances neceflary to infure its fuccefs. In particular, the inventor ftates that the 

 marine acid of commerce is unfit for this purpofe. 



This^acid was formerly prepared with the marine fait of the faltpetre manufadurers ; 

 and even when it is made with good fait, the decompofition is effefted with common vi- 

 triolic acid which contains nitrous acid. Marine acid mixed with a fmall quantity of 

 nitrous acid does not prevent the filk from being beautifully whitened : it even accelerates 

 the procefs confiderably, and in the moft fatisfadory manner. But the alcohol, every time 

 it is ufed and redified, becomes charged with the acid and gas of nitre, which afl^ume the 

 charaaers of the nitrous anodyne liquor. In this ftate, neither diftillations nor repeated 

 rcaifications from alkali are fuflicient to feparate the nitrous matter from the alcohol. 

 Then it is that the fuccefs of the operator vaniflies, with a degree of rapidity equal to the 

 advances wliich encouraged his hopes at the commencement. The fame difappointments 

 bcfel M. Baumc- at the beginning of liis labours ; to prevent which, he direds the prepa- 

 ration of the vitriolic and marine acids to the following eftea. 



The vitriolic acid of commerce is obtained by burning fulphur in chambers of lead, with the 

 addition of faltpetre, either crude or of the fccond cryftallization, and a fmall portion of 

 flax. This acid is concentrated and reaified in France, at the place of its fabrication, to 66 

 degrees of Baume's hydrometer, or fpccific gravity in the ufual form 1.848. It contains 

 fulphur, lead, vitriolatcd tartar, Glauber's fait, alum, fclcnite, and particularly the nitrous 

 and marine acid. 



Vol. I.— iViAY 1797. N To 



