EXPERIMENTS ON ASTRINGENT VEGETABLES. 271 



about 1.39. The extract from Bengal is more friable, and left 

 confident; its colour is like that of chocolate externally, but, 

 when broken, its fracture prefents ftreaks of chocolate and of 

 red-brown. Its fpecific gravity is about 1.28. Their tafies 

 are precifely fimilar, being aftringent, but leaving in the mouth 

 a fenfation of fweetnefs. They do not deliquefce, or appa- 

 rently change, by expofure to the air. 



The difcovery of the tanning powers of catechu, is owing to Sir J. Bank* 

 the Prefident of the Royal Society, who, concluding from its J^iJ^jJjJ, 

 fenfible properties that it contained tannin, furnilhed me, intanin. 

 December, 1801, with a quantity for chemical examination. 



In my firft experiments, I found that the folutions of catechu Experiments 

 copioufly precipitated gelatine, and fpeedily tanned (kin ; and, *?* ™* trutil 

 in confequence, I began a particular inveftigation of their clufion. 

 properties. 



The llrongefl infufions and decoctions of the two different Both kinds agree 

 kinds of catechu, do not fenfibly differ in their nature, or in &Ct ' 



their composition. Their colour is deep red-brown, and they 

 communicate this tinge to paper; they (lightly redden litmus- 

 paper ; their tafte is highly aftringent, and they have no per- 

 ceptible fmell. 



The ftrongefl infufions that I could obtain from the two kinds The ftrongcft 

 of catechu, at 4S° Fahrenheit, were of the fame fpecific gra-^^ ™ of 

 vity, 1.057. But, by long decoction, I procured folutions of 

 1.102, which gave, by evaporation, more than £ of their 

 weight of folid matter. 



Five hundred grains of the ftrongeft infufion of catechu from afforded 41 foJid 

 Bombay, furnilhed only 41 grains of folid matter; which, JSJ^S'Jt 

 from analyfis, appeared to confift of 34 grains of tannin, or7 peculiar ex* 

 matter, precipitable by gelatine, and 7 grains that were chiefly tra " # 

 a peculiar extractive matter, the properties of which will be 

 hereafter defcribed. The quantity of folid matter given by the 

 ftrongeft infufion of the Bengal catechu, was the fame, and 

 there was no fenfible difference in its compofition. Portions 

 of thefe folid matters, when incinerated, left a refiduum which 

 feemed to be calcareous; but it was too frnall in quantity to be 

 accurately examined, and it could not have amounted to more 

 than j^ of their original weights. 



The ftrongeft infufions of catechu acted upon the acids and The Infufion 

 pure alkalis in a manner analagous to the infufion of galls. acATand alk^S* ; 

 With the concentrated fulphuric and muriatic acids, they gave 



denfe 



