OB VEGETABLE ASTRINGENTS. . gflj | 



sideling what are the characteristic properties of extract, as 

 stated at full length by Mr. Vauquelin; for we shall find, 

 that, so far from marking any essential difference between 

 this substance and tan, they are equally applicable to the 

 latter, and have been pointed out as even peculiar to it. 

 Among these we may notice its solubility in water and al- 

 cohol*, its strong taste, the effect of oximuriatic, nitric, 

 sulphuric, and muriatic acids, of alkalis, and of metallic 

 oxidesf. 



Are we then to conclude, that the infusion of galls does Does the infu- 

 not contain any constituent, to which the title of extract nothhTg but 

 ought to be applied ? or that, according to the original opi- gallic acid and 

 nion of Proust, Seguin, and others, the infusion consists 

 merely of tan and gallic acid ? Upon this point I do not 

 feel myself qualified to give a decisive opinion. Although 

 I think the proofs, that have been adduced in favour of the 

 existence of extract, are very insufficient, that we are not 

 yet in possession of any method of accurately recognizing 

 its presence, and that we are unable to say what are its cha- 

 racteristic properties ; j r et I do not conceive, that we are 

 warranted in denying its existence. There is indeed one Fact in favour 

 fact which seems a strong presumption in its favour, viz. enceo f^ l t S raet- 

 that, if we take two portions of the same infusion of galls, 

 and saturate one of them with jelly, and the other with the 

 oximuriate of tin, and let each of them remain for some 

 time exposed to the atmosphere, until they have deposited 

 all their precipitates, they will then each of them afford 



* Tan is insoluble in perfectly pure alcohol, but it is readily dissolved 

 in the alcohol with which our experiments are usually performed. 



•f It is stated, that extract is insoluble in ether; but this does not ap- 

 ply to that part of the infusion of galls, which is acted on by the oxi- 

 muriate of tin, for this reagent forms a copious precipitate with a solu- 

 tion of the substance which is left by evaporating ether that has been 

 digested on galls. This substance appears indeed to act as readily upon 

 the oximuriate of tin as wpon jelly or gallic acid, and I could not per- 

 ceive, that it differed in any respect from the substance procured from 

 the aqueous infusion of galls, except in being lighter coloured. Mr. 

 Murray observes (a), that the colouring matter of saffron, which' has 

 keen regarded as a specimen of pure extract, is readily soluble in ether. 



(a} Chemistry, IV, 264. 



