ON VEGETABLE ASTRINGENTS. 243 



of alcohol or ether; in both these cases, after the action of 

 these fluids has been carried to its fullest extent, a residuum 

 is left, upon which water has no action, yet mucilage is in- 

 Soluble both in alcohol and in ether. I feel it necessary to 

 apologize for differing from Mr. Davy on this point of fact, 

 but I may say in my excuse, that lie relates the process for 

 obtaining the mucus of galls rather as one calculated to 

 answer the end in view, than as what he had really put in 

 practice. That portion of the galls, which in his analysis 

 he attributed to mucus, I shouid refer principally to the 

 imperfect compound of tan and jelly, which I have described 

 above. 



I shall now make a few observations on the chemical pro- Catechii very 



perties of catechu ; but it is necessary to premise, that the va "" b . le uuts 

 ...... ,,., qualities. 



Varieties in this substance are even greater than those in the 



gull nut. That which I employed was considered by a 

 friend, on whose judgment I could rely, as a good specimen 

 of the kind which is most esteemed by the apothecaries ; 

 yet from my experiments with it, it seemed to differ from 

 that employed by Mr. Davy. Cold water being digested Treated with 

 upon it for two days took up T V of its weight; the solution co w * er ' 

 was transparent, and of a tine reddish brown colour; the 

 portion which remained undissolved seemed like a mixture 

 of white and red particles, in which the white considerably 

 predominated, but when it was dried its colour became as 

 deep as that of the catechu in its recent state. The solu- 

 tion slightly reddened litmus; it was rendered turbid by the 

 oxalate of ammonia, and a small quantity of a dense pre- 

 cipitate subsided from it. It was also liable to the opera- 

 tion of moulding, although not so readily as the infusion 

 of galls. When catechu is ti*eated with hot water, it is and wiih hoV 

 partly dissolved and partly suspended. An opake infusion 

 is formed, which contains about T V of its weight of so- 

 lid matter* The warm infusion still continues quite opake 

 after being passed through a paper filter, while the filter 

 gains a great addition of weight, and is stiffened as if it had 

 been soaked in some kind of mucilaginous matter. By 

 standing for some days, a part of the contents is deposited,, 

 and the warm infusion beeomes transparent. If the clear 

 solution be evaporated, the residue is not capable of being 

 R 2 completely 



