On an artificial tanning Siilstance. 173 



cannot fell to rentier the instrument iu some small measure 

 mure sensible, and, so tar as it eoes, to counteract the slug- 

 gishness produced bv any increased tenacity in the fluid. 



But as the body of the instrument is made of glass, the 

 amount of the contraction must be very small, and the 

 change of senslbilitv arising from it so very trifling, as cer- 

 tainly by no means to obscure such an eflect as an increase 

 of tenacity would occasion. I therefore with some confi- 

 dence conclude, that the fluidity of the water is not sensibly 

 diminished, and consequently that the polarity has not be- 

 gun to exert any sensible influence ; it can scarcely, there- 

 fore, be accounted the cause of the dilatation. 



XXXVI. On an arfi/icial Substance which possesses the prin- 

 cipal characteristic Propertits of Tannin. By Charles 

 Hatchett, Esq. F.R.S.* 



§ I. 



J. HE discovery of the principle on which the eflfects of 

 tanning essentially depend, may be partly attributed to M. 

 Deveux, who obtained a substance from galls which he 

 considered as a species of resin f, but which was afterwards 

 proved by M. Seguiu to be that which renders the skins of 

 anin)als insoluble in water and imputrescible, and thus to 

 be the principle bv which they are converted into leatherj. 



The chief characteristic property of this substance was 

 ascertained by M. Scguin to be that of precipitating gela- 

 tine or glue from water in a state of insolubility : and as it 

 was evidently diflferent from any vegetable substance hitherto 

 discovered, he gave it the name of tannin. 



This discovery of M. Scguin at once unveiled the theory 

 of the art ; an easy and certain method was afl^'orded by which 

 tannin could be detected, and its relative quantity in dif- 

 ferent substances be determined, whilst the nature and pro- 

 perties of this newly discovered vegetable principle could be 

 subjected to accurate investigation. 



The former has derived elucidation from the experiments 

 of Mr. Bi:igin§, and n)uch has been contributed in every 

 respect by M. Proust ||; but the subject has received the 



• Pram the TransacTiotu of the Royal Society for 1805. 



f Mitmutrr sur la Nvu de Oaik, par M. Ueyeux; Annahs de Chimie, 

 tomt' xvii. p 'is. 



\ Ibid, tome XX. p. 15. § Phil. Trans. 179% p. ?59. 



I' AiiiiaUs lie Ctuin,c, tome xxv. p. ^25. IbiJ. tum« xJi. p. 331. Ibid. 

 ilii. p. \i9. 



2 greatest 



