ON VEGETABLE ASTRINGENTS. ' g]j 



Fatter in my experiments. In operating with the" 6'xirhtii agent for as- 



riitte of tin there is a circumstance to be attended to, which tnn § cnl inf "«* 



sions. 

 may interfere with the results ; when the aqueous solution 



of this salt is very much diluted, it becomes insoluble, and 



a precipitate is formed, which in experiments on vegetable 



infusions might be mistaken for the effect of a combination butitis preci- 



of the oxide of tin with some of the constituents of the sub- P ltatcd Jy . 



great dUuuare. 

 stance under examination. The precipitate seems in this 



case to depend upon the water removing a quantity of super- 

 abundant acid, which is necessary to render the salt soluble 

 in water*. Having had occasion to make frequent use of 

 the oximuriate of tin as a reagent, I wished to ascertain what 

 degree of minuteness it possessed as a test for tan or extract, 

 and for this purpose, an infusion was formed by macerating "sdelicuf ii 

 a quantity of finely powdered galls in eight times their 

 weight of cold water for twenty-four hours. Portions of 

 this infusion were successively added to 10, 20, 30, 40, and 

 50 times their weight of water, and even in the last in- 

 stance the oximuriate of tin caused a slight precipitate, but' 

 no effect could be perceived when the infusion was mixed 

 with 100 times its weight of water. The nitromuriate of 

 Jin seems to be nearly as delicate a test, and they are both 

 considerably more so than the simple muriate. 



I have had occasion to refer to the effects, that are pro- Twelve suc- 

 duced by subjecting the same portion of galls to a number s^nTof the" 

 of successive infusions, and I shall now describe these effects same galls at * 

 a little more fully. A quantity of finely powdered galls was 0Iillj » " at " 

 infused in ten times its weight of water, kept at the boiling 

 heat for an hour, and then suffered to ftand until the follow- 

 ing day, when the fluid was drawn off; the same quantity of 

 water was then added to the residue, which was boiled as 

 before, and the Operation was repeated for twelve succes- 

 sive days. This twelfth infusion was colourlefs, it afforded 

 mo precipitate with jelly or the oximuriate of tin.; and only 

 a slight gray tinge with the oxisulphate of iron. These in- 

 fusions were kept for a fortnight, and were then examined. 

 The first infusion contained a large quantity of sediment, 

 and was covered with a thick coating of mould. The 2d 



* lerthollet, Stat. Chim. II, 457. 



P 2- mi 



