EXPERIMENTS ON ASTRINGENT VEGETABLES, 33 



precipitated gelatine, and contained a portion of the vegetable 

 principles, and a certain quantity of fuipliate of lime ; a folid 

 fawn-coloured matter was likewlfe formed, which appeared 

 to be fulphate of lime, united to a Utile tannin and extraftive 

 matter.* 



The folutions were copioufly precipitated by folutlon of al- Copious precipi- 

 , t ^ I r J tations by albu- 



bumen. ... "'^"• 



The precipitates they gave with gelatine were (imilar in their 

 appearance ; their colour, at firft, was a light tinge of brown, 

 but they became very dark by expofure to the air. Their com- 

 pofition was very nearly fimilar ; and, judging from the ex- 

 periments on the quantity of gelatine employed in forming them, 

 the compound of tannin and gelatine from the ftrongeft inFufiou 

 of oak bark, feems to confift, in the 100 parts, of 59 parts of 

 gelatine and 41 of tannin ; that from the mfufion of Leicelier 

 willow bark, of 57 parts of gelatine and 43 of tannin ; and that 

 from the mfufion of Spanifli chefnut bark, of 61 parts of gela- 

 tine and 39 of tannin. 



Two pieces otcalf-fkin, which weighed when dry 120 grains Experiments of 

 each, were tanned ; one in the ftrongeft infufion of Leicefter '^^"?'"f ^'" 



' » with the intu« 



willow bark, and the other in the ftrongeft infufion of oak bark, iions of barks. 

 The procefs was completed, in both inftances, in lefs than a 

 fortnight ; when the weight of the leather formed by the tannin 

 of the Leicefter willow bark was found equal to 161 grains; 

 and that of the leather formed by the infufion of oak bark was 

 equal to 164 grains. 



When pieces of fkin were fuffered to remain in fmall quan- Spent ouze ox 

 litiesof the infufions of the oak bark, and of the Leicefier wil-'"-''"''°"* 

 low bark, till they were exhaufted of their tanning principle, 

 it was found, that though the refidual liquors gave olive-colour- 

 ed precipitates with the folutions of fulphate of iron, yet they 

 were fcarcely rendered turbid by folutions of muriate of tin; 

 and there is every reafon to fuppofe, that a portion of their ex- 

 tradive matter had been taken up with the tannin by the Ikin. 



* M. Merat Guillotpropofes a method of procuringpure tannin, 

 (Annales de Chimie, Tome XLI. p. 325.) which confilts in pre- 

 cipitating a folution of tan by lime-water, and decompofing it by 

 nitric or muriatic acid. The iulution of the folid matter obtained 

 in this way in alcohc;!, he cr.fi lers a^ a folution of pure tannin j 

 but, from the experiments above-meruionec', it appears, that it muft 

 contain, belidts lanuin, fome of the extraftive matter of the bark j 

 and it may likcwife contain faline matter. 



Vol. VI. — September. B I at" 



