368 ON ARTIFICIAI, TANNIN. 



thrown dowu. I then poured off the liquid, which was of 

 a light yellow, and washed the precipitate with a great deal 

 of water. 



4. This precipitate, which was a compound of the tan* 

 ning matter and oxide of lead, was thrown still wet into 

 water acidulated with sulphuric acid. After boiling I left 

 these substances to act on each other for twenty-four hours. 

 At the expiration of this time I satisfied myself by means 

 of barytes water and sulphuretted hidrogeri, that there was 

 neither sulphuric acid nor lead in the solution. 

 Its properties. I filtered the liquor to separate the sulphate of lead, and 

 evaporated it to dryness. A brown mass remained, which 

 melted by heat, hardened on cooling, and afterward at- 

 tracted moisture from the atmosphere. The aqueous solu- 

 tion of this substance reddened litmus, and formed a pre- 

 cipitate with gelatine, barytes water, and acetate of lead. 

 The precipitates with the latter two were soluble in nitric 

 acid; and melted when exposed to heatin aglass tube closed 

 at one extremity, emitting an aromatic smell mixed with 

 something of the prussic. When operating on the precipi- 

 tate with lead, if the residuum were thrown on a paper 

 while hot, it took fire like a pyrophorus. This combustion 

 was produced by charcoal and metallic lead in a state of 

 minute division. The residuum of the compound with ba- 

 rytes was very little pyrophoric. 

 Examination of 5. To ascertain whether any nitric acid were present in 

 it for nitric t ne tanning matter prepared by the preceding process, I in- 

 troduced 5 dec. [7-7 grs] into the glass bulb, and heated 

 them. The matter fused, because it contained a little hu- 

 midity; and evolved with much impetuosity aqueous vapour, 

 ammonia, carbonic acid, nitrous gas, &c. A coal remain- 

 ed, that emitted a strong smell of prussic acid. 

 Combination of 6. As I tried the preceding experiment several times, I 

 it with sulphu-£ oun( j^ t } jat su ]p niir i c acid was capable of combining with 

 the tanning matter, when it separated it from oxide of lead ; 

 and that this compound, when it did not contain an excess 

 of sulphuric acid, formed with barytes a precipitate solu- 

 ble in nitric acid, and gave out sulphuric acid when heated. 

 It seemed to me, that by boiling carbonate of lead wilh this 

 compound dissolved in water, evaporating to dryness and 



redissolving 



