ON ARTIFICIAL TANNIN. ^ 369 



Tcdissolving in water repeatedly, the oxide of lead united 

 with the sulphuric acid, and a substance was obtained, which 

 when heated no longer gave out any sensible quantity of 

 sulphurous acid. This experiment I performed but once. 



7. The liquor, from which the tanning matter had been Amer found in 



separated by acetate of lead, had sulphuretted hidrogen ^e liquid from 



r J ' * ° which the tan- 



passed through it; after which it was filtered, and evapo- n in had been 



rated to dryness. The residuum was dissolved in water, and se P arated - 

 potash was added to the solution. This produced a yellow 

 precipitate of lime retaining some bitter matter. The liquor 

 being filtered and concentrated yielded silky crystals, of a 

 golden yellow colour, detonating, and resembling those 

 formed by Welther's amer and potash. Proust had already 

 observed, that a small quantity of this substance was form- 

 ed, when pitcoal was treated with nitric acid at 40^ [sp. gr. 

 1-396]. 



Hence it follows, that the matter soluble in water is Nature of the 

 formed, 1st, of a substance that precipitates gelatiue copi- compoun ' 

 ously, which is a compound of nitric acid, and carbona- 

 ceous matter; 2d, of a very small quantity of amer at a 

 maximum. The acetate of lead forms with the first a com- ' 



pound insoluble in water, and with the second a compound 

 soluble in it. 



Art. II. Examination of the matter A. 



8. The matter A, after it had been several times washed, Examination of 



was of the colour of umber. It had a slightly acid taste: '^difficultly 



b J ' soluble matter. 



and reddened litmus paper on which it was moistened with . 



a little water. Heated in a glass tube it melted, emitting a 

 red light, and a smell of nitrous acid mixed with prussic. 

 To destroy the supposition, that the nitrous acid might have 

 arisen from the remains of the acid that escaped the waters 

 of elutriation, I digested the matter A in water, filtered, 

 and washed it repeatedly with fresh water. Of the sub* 

 stance thus washed I heated 2 dec. [3 grs] in the glass bulb. 

 The matter fused, and gave out, 1st, water; 2d, nitrous 

 vapour; 3d, carbonic acid; 4th, ammonia; 5th, some in. 

 flammable gas, which appeared to me a mixture of oily hi- 

 drogen and gaseous oxide of carbon, for it burned with a 

 heavy white flame, and presently with a blue; 6th, nitrous 

 Vol. XXXII. Supplement. 2 C gas ; 



