122 Memoir upon the Co7ivcrsion of ligneous Bodies into 



plunged in a sand-bath, it decomposes and becomes black a little 

 before the water begins to boil. When treated in this state with 

 a little water, flocculi of vegetable matter partly carbonized are 

 separated ; and when some nitrate of barytes is poured into the 

 liquor, an abundance of sulphate of barytes is precipitated. When 

 this acid is subjected to a temperature higher than that of boiling 

 water, its decomposition is more rapid, and suffocating vapours 

 of sulphurous acid are emitted. This acid does not produce any 

 change on metallic solutions. Nitrate of barytes and sub-acetate 

 of lead are not in the least affected by it. It makes a strong 

 effervescence with carbonates, and appears to dissolve all the mc- 

 taUic oxides, with which it forms salts, uncrystallizab!*, deliques- 

 cent, insoluble in acetified alcohol. These saline and neutral 

 combinations, subjected to fire, decompose, emit sulphurous acid, 

 and leave sulphates and charcoal. The same acid dissolves iron 

 and zinc, liberating abundance of oxygen gas. It forms with 

 oxide of lead and barytes very soluble salts, which have a giimmy 

 appearance. It seems to have a strong enough dissolving fa- 

 culty ; for it even dissolves to a certain degree sulphate of lead. 

 This acid is composed of sulphur, carbon, hydrogen and oxy- 

 gen ; or of a vegetable matter, and the elements of sulphuric 

 acid, but in proportions with which I am unacquainted. 



Action of Sulphuric Acid on Silk. 



In treating silk with sulphuric acid, I conceived the hope of 

 returning it to its primitive state of silky liquor, such as is ex- 

 tracted from the bodies of certain caterpillars, and with which, 

 according to Reaumur, the Mexicans prepare their admirable 

 varnish. I hoped by means of a similar liquor artificially prepared 

 with pieces of silk, that it would be easy to fabricate cloth not 

 spun. I have not however obtained this result, though I have 

 not abandoned the hope of attaining it. Be this as it may, the 

 sulphuric acid can convert the silk into two mucilaginous sub- 

 stances very distinct. 



If some pieces of white silk are slightly moistened with this 

 acid, and, after a few minutes have been given to allow it to act, 

 the mixture is treated with a quantity of water, a very thick 

 white mucilage is obtained resembling gum tragacanth. When 

 a greater quantity of water is added, the whole of the mucilage 

 is precipitated, and the surnatant liquid, which is as colourless as 

 pure water, retains only a small quantity of silk in solution. This 

 mucilage well washed with water is insipid to the taste. It is 

 not sensibly affected by cold water ; but a great quantity of boil- 

 ing water dissolves it : the liquor being evaporated, there remain 

 some insoluble membranes : an infusion of nut-galls produces a 



precipitate. 



I 



