ON VEGETABLE ASTRINGENTS. g4J 



much in different specimens. About | of the catechu 

 seems insoluble in this menstruum. This part was readily 

 taken up by water, except a small dark-coloured residuum; 

 the solution produced only a slight effect upon jelly and 

 the oximuriate of tin, but by the oxisulphate of iron the 

 whole became as it were coagulated, and was converted into 

 a gray mass. The acetate of lead also threw down a very 

 copious precipitate from the fluid. These properties denote 

 a considerable analogy between this part of the catechu, 

 and the mucilaginous bodies, an analogy which is farther 

 strengthened by a degree of viscidity, which may be ob- 

 served in its solutions. The substance obtained by evapo- 

 rating the spirituous solutions of catechu is of a deep 

 red colour, soluble in water but less so than the whole ca- 

 techu ; the solution is •copiously precipitated by jelly, by the 

 oximuriate of tin, and the oxisulphate of iron. It moulded 

 by exposure to the atmosphere, I think, rather more readily 

 than the entire catechu. 



The infusion of catechu is very 'Copiously precipitated by Action of re- 

 jelly, but a part of the precipitate generally remains sus- ^fusion." 

 pended in the fluid. The oximuriate of tin also acts pow- 

 erfully upon catechu, but it is not much -affected by tar- 

 tarized antimony, it is rendered opake, and the brown colour 

 is changed to red, but scarcely any precipitate is formed. 

 The acetate of lead exercises thy same instantaneous action 

 on catechu as on galls-; it immediately unites with all the 

 constituents of the infusion, and leaves the fluid perfectly 

 transparent and colourless. The nitromuriate of gold 

 throws down a very copious precipitate of a blackish purple 

 colour, and the nitromuriate of platina an equally copious 

 one of a deep reddish brown. The precipitate produced by 

 the oxisulphate of iron is of a deep olive green, and readily 

 subsides from the fluid. This precipitate must, I appre- 

 hend, be considered as an obvious indication of a small 

 quantity of gallic acid ; and m»y therefore be regarded as 

 a proof of the variety, which exists in different species of 

 this substance, since that which Mr. Davy employed was 

 without this constituent*. J have always found the infu- 



* Philos. Trans. 180.% p. ?69, 



