270 



EXPERIMENTS ON ASTRINGENT VEGETABLES'* 



fulphate of iron, than an equal portion of a fimilar infufior! 

 which had been immediately precipitated by folution of 

 ifinglafs ; but I am inclined to attribute this effect, not to any 

 abforption of gallic acid by the fkin, but rather to the decom- 

 position of it by the long continued action of the atmofpkere j 

 for much infoiuble matter had been precipitated, during the 

 procefs of tanning, and the refidium contained a fmall portion 

 of acetous acid. 



Component parts In ascertaining the quantity of tannin in galls, I found that 



•f Aleppo gallc ajqq g ra i ns f g 00( j Aleppo galls gave, by lixiviation with pure 

 water till their foluble parts were taken up, and fubfequent 

 flow evaporation, 185 grains of folid matter. And this matter* 

 examined by analyfis, appeared to confift, 



Solid matter. Of tannin .--.-„ 130 grains. 



Of mucilage, and matter rendered infoiuble by 

 evaporation - - - - - -12 



Of gallic acid, with a little extractive matter 3 1 



Remainder, calcareous earth and faline matter 12 



JUfidual fluid. The fluid obtained by the laft lixiviation of gulls, as M. Deyeux- 

 obferved, is pale green ; and I am inclined to believe, that it 

 ' v is chiefly a weak folution of gallate of lime. The afhes of galls, 

 deprived of foluble matter, furnifh a very considerable quantity 

 of calcareous earth. And the property which M. Deyeux 

 discovered in the liquor of the laft lixiviations, of becoming 

 red by the a&ion of acids, and of regaining the green colour 

 by means of alkalis, I have obferved, more or lei's, in all the 

 foluble compounds containing gallic acid and the alkaline 

 eaTths. 



III. EXPERIMENTS AND OBSERVATIONS ON CATECITU 

 OR TERRA JAPONICA. 



Catechu or terra The extract called catechu is faid to be obtained from the^ 

 japomca. WO od of a fpecies of the Mimofa *, which is found abundantly 



in India, by decoction and fubfequent evaporation. 

 Hiftory and ex- There are two kinds of this extract ; one is fent from Bom- 

 tcrnal characters ^ the ()tner f rom ]3 enga l . an d they differ from each other 

 from Bombay J . , . , 1} . , . . . , 



acwi Bengal. more in their external appearance than in their chemical com- 



pofition. The extract from Bombay is of an uniform texture, 

 and of a red-brown tint, its fpecific gravity being generally 



See Kerr. Medical Obfervations, Vol. V. p. 155. 



about 



