t 212 ] 



XXXVI. y}/i Account of' soyne Expcrii/ienls and Observa- 

 tions on the constifi/cnt Parts of certain astringent Vege- 

 tables ; and on their Operation in Tanning. By Hum- 

 PHRV Davy, Esq. Professor of Cheinistri/ in the Royal 

 Tnslitution, 



[Ci'Utiiuicd from p. 76.] 



III. Experiments and Obsrrrations on Catechu or Terra 

 Japonica. 



JL HE extract called catechu is said to be obtained from the 

 \vood of a species of the ntiniosa *, which is found abun- 

 dantly in India, by decoction and subsequent evaporation. 



There are two kinds of this extract; one is sent from 

 Bombay, the other from Bengal ; and they differ from each 

 other more in their external appearance than in their che- 

 mical composition. The extract from Bombay is of an 

 imiform texture, and of a red brown tint, its specific gra- 

 vity being generally about I'Sg. The extract from Reng.al 

 is more friable, and less consistent ; its colour is like that 

 of chocolate externally, but, when broken, its fracture pre- 

 sents streaks of chocolate and of red brown. Its specific 

 gravity is about 1*28. Their tastes arc precisely similar, 

 icing astringent, but leaving in the mouth a sensation of 

 sweetness. They do not deliquesce, or apparently change, 

 bv exposure tu the air. 



The discovery of the tanning powers of catechu is owing 

 to the president of the Royal Society, who, concluding from 

 its sensible properties that it contained tannin, furnished 

 me, in December ISOl, with a quantity for chemical exar 

 mination. 



In my first experiments, I found that the solutions of 

 catechu copiously precipitated gelatine, and speedily tanned 

 skin; and, in consequence, I began a particular investiga- 

 tion of their pi'operties. 



The strongest infusions and decoctions of the two dif- 

 ferent kinds of catechu do not sensibly differ in their na- 

 ture, or in their ^composition. Their colour is deep red 

 brown, and they connnunicate this tinge to paper; they 

 slightly redden litmus paper; their taste is highly astrin- 

 gent, and they have no perceptible smell. 



The strongest infusions that I could obtain from the two 

 kinds of catechu, at 48° Fahrenheit, were of the same spe- 

 cific gravity, 1'057 : but, by long decoction, I procured so- 



'* Sec Kerr. Medical Observations, vol. v. p. 155. 



lutioi»a_ 



