Substance possessing the Properties of Tannin. 1 55 



experiment, in which a pyrometer-piece was placed withiu 

 the barrel, and another in the muffle ; they agreed in indi- 

 cating 23°. The inner tube, which was of Reaumur's porce- 

 lain, contained eighty grains of pounded chalk. The carbo-» 

 nate was found, after the experiment, to have lost 3-^ grains. 

 A thin rim, less than the 20th of an inch in thickness, of 

 whitish matter, appeared on the outside of the mass. In 

 other respects the carbonate was in a very perfect state j it 

 was of a yellowish colour, and had a decided semi-transpa- 

 rency and saline fracture. But what renders this result of 

 the greatest value is, that on breaking the mass a space of 

 more than the tenth of an inch square was found to be com- 

 pletely crystallized, having acquired the rhomboidal fracture 

 of calcareous spar. It was white and opake, and presented 

 to the view three sets of parallel plates which are seen under 

 three different angles. This substance, owing to partial cal- 

 cination and subsequent absorption of moisture, had lost all 

 appearance of its remarkable properties in some weeks after 

 its production; but this appearance has since been restored 

 by a fresh fracture, and the specimen is now well preserved 

 by being hermetically inclosed. 



[To be continued.] 



XXV. Additional Experiments and Remarks on an arti- 

 Jicial Substance which possesses the principal characterislic 

 Properties of Tannin. By Charles Hatchett, Esq. 

 F. R. S. 



[Concluded from p. 68.] 



§ VII. 



x* ROM the experiments which have been related, it appears, 

 that three varieties of the artificial tanning substance may be 

 formed, viz. 



1st, That which is produced by the action of nitric acid 

 upon any carbonaceous substance, whether vegetable, am» 

 mal, or mineral, 



2dly, That which is formed by distiUipg nitric acid from 



comiiaon 



