r 0N ARTIFICIAL TANNIN* 373 



matter separated, which I shall examine below. Theliquot 

 freed from this was evaporated to dryness; The residuum, 

 was black, a little astringent, and slightly acid. Heated in 

 a. glass tube, it did not melt, but an acid vapour was evolved. 

 The greater part dissolved in distilled water. This solution 

 precipitated gelatine, and many metallic salts. The preci- 

 pitate formed with acetate of lead, being heated in a glass 

 tube, left a coal mixed with metallic lead, which took fire, 

 if thrown on paper while hot. 



41. To obtain the tanning matter in a state of purity, I Purified, 

 precipitated the solution by acetate of lead, and washed the 

 precipitate, till the water that came off ceased to be colour- 

 ed by sulphuretted hidrogen. I decomposed the precipi- 

 tate, while yet wet, by sulphuric acid. The sulphate of 



lead was separated by the filter. With barytes and acetate 

 of lead the liquor threw down a flocculent precipitate, so- 

 luble in an excess of nitric acid; which indicated, that it 

 contained no sensible excess of sulphuric acid*. How- and examined. 

 ever, having evaporated to dryness, I obtained a brown, 

 deliquescent residuum f , fusible by heat; which, being 

 heated in the glass bulb, gave out carbonic acid gas, sul- 

 phurous acid gas, and other gaspes insoluble in water, which 

 I was unable to examine from the smallness of their quan- 

 tity (for I operated only with 2 dec. [3 grs] of tanning 

 matter); so that I know not whether any nitrous gas were 

 among them. 



42. Thus it appears, that, when the compound of tart- Sulphuric add 

 ning matter and lead is decomposed by sulphuric acid, the c ° mbines Wlth 



matter. 



* To find whether a liquid contain any excess of sulphuric acid> Barytes recom- 

 solution of barytes should be poured into it. If a precipitate form, mended as a 

 try to dissolve it in pure nitric acid. If this dissolve it, the matters ri( ! acid u P u " 

 should be left to act on each other for 24 hours, and then see whe- 

 ther there be any precipitate. I have often observed that lead in- 

 dicated no sulphuric acid, where barytes did perceptibly. The lat- 

 ter therefore is preferable as a test to the former. 



•f I have found, that by heating this residuum a little strongly 

 in contact with the air in a capsule white fumes of sulphuric acid 

 were evolved; and the substance thus heated; being redissolved in 

 water, gave indications of sulphuric acid, when tested with solution 

 •f barytes. 



latter, 



