ON VEGETABLE ASTRINGENTS. 



sor 



colour; potash throws down a very minute precipitate from 

 the acid, while the residue is rendered quite black, and 

 strongly resembles charcoal powder ; a circumstance which 

 seems to show, that the blackness of charcoal is not neces- Blackness of 

 sarily connected with the the process of combustion or oxid- connected * 

 ation. with oxidation. 



In forming infusions of galls it occasionally happens, that Green tinge of 

 we obtain them of a bottle-green hue. Mr. Deyeux and tbe infusloa 

 Mr. Davy both mention this as occurring in the latter in- 

 fusions, where the same galls have had repeated quantities 

 of water poured on them*; but it never occurred to me to 

 observe the green colour under these circumstances, while, 

 on the contrary, I have met with it in an infusion of fresh 

 galls, where no shade of green could be observed in any of 

 the subsequent infusions. It is attributed by Mr. Deyeux 

 to a green colouring matter, which he enumerates among 

 the constituents of the galls ; while Mr. Davy ascribes it to not owing to 

 the gallate of lime. My observations lead me to question * e 8 a,Iate •* 

 the accuracy of this latter opinion. In the first place it 

 seems an almost decisive objection to it, that, if lime water 

 be added in small quantities to the recent infusion of galls, 

 so that the tan be not precipitated, the green colour is not 

 produced ; yet in this case the lime must be employed in 

 saturating the uncombined gallic acid, and thus forming the 

 gallate of lime. In one of the greenest infusions that I ever 

 procured, the oxalate of ammonia did not produce the least 

 effect, while the subsequent addition of the most minute 

 portion of lime water immediately caused the precipitation 

 of the oxalate of lime. If to the infusion of galls pure pot- Effect of re- 

 ash be added, the brown colour is at first rather increased, a ? enCs in pro- 



ducing or re- 

 but after some time a shade of green becomes visible. The moving the 



effect is much more speedy and more decisive where the K reen ttnge- 

 carbonate of potash is employed; a similar effect is pro- 

 duced by lime water, except that the green is more of the 

 gluceous hue. In all these cases the green colour is instantly 

 removed by an acid; where potash has been employed the 

 fluid acquires a reddish tinge, and where lime water was 

 used, a delicate violet. The green colour always disappears 



* Deyeax, ubi supra, p. 12 ; Davy, ubi supra. 



