2Q5 ON VEGETABLE ASTRINGENTS. 



in the analysis of vegetables, and have been generally as- 

 ( I to the extractive principle, which is said to become 

 insoluble by the absorption of oxigen*. It seems, that in all 

 Galls should cat-es, the more finely the gall nuts are powdered, the 

 be finely now- stronger is the infusion, which equal weights will produce. 

 Sue essivc in- ^ consl derable proportion of the gall-nut is soluble in 

 fusions neces- water, but for this purpose it is necessary, that several sue- 

 SWi cessive infusions be employed. Water will readily take up 



T V of its weight of the so ruble part of the gulls f; and yet if 

 a quantity of the powder be infused with 20 times its weight 

 of water, a 2d quantity will extract something which had 

 escaped the first infusion. This circumstance is particu- 

 larly noticed by Trommsdorf; for although he infused galls 

 for three days in above twelve times their weight of water, 

 yet it required four of these infusions to remove all the solu- 

 ble matter I. The proportion of matter, which remains in- 

 soluble after these successive infusions, has been very va- 

 riously eftimated. Mr. Deyeux speaks of the insoluble 

 part as a very small quantity, without stating its amount § ; 

 Proportion of while Mr. Davy informs us, that he had 3 15 parts left out 

 insoluble mat- f 500> or near i y | f the whole II. In four different trials 

 ter. , 



which I made with a good deal of care, I found the residues 



to be in the different cases nearly as f, -£-, T \r, and T ' ? of the 

 whole. In these experiments the number of successive in* 

 fusions was from 12 to 14, and the quantity of water em- 

 ployed at each infusion was ten times the weight of the ori- 

 Action of re ginal quantity of galls. What is left is a dark coloured and 

 agents on it. narc | }j c|y } U p n which alcohol and the caustic alkalis have 

 no action. Muriatic acid, by being boiled on it, breaks it 

 down into small pieces, and is itself tinged of a light brown 



* Fourcroy, Analyse de Quinquina, Ann de Chim. VIII, 122. & alibi* 



Systems, VI!, 312. 



Davy, Philos. trans. 1303, p. 237. 



Thomson's Chem. V, 107. 



Atkins' Dictionary, Art. Extract, p, 422. 

 T Mr. Davy formed infusions, which contained between I-7th and 

 1-8th of their weight of solid matter. Phil. Trans. 1803, p. ^40. 

 % Thomson's Chemistry, II, S5j. 

 § Ann.de Chim. XVII, 11. 

 ft Phil. Trans. 1S03, p.351. 



colour ; 



