296 Experiments dnd Ohsenations on the 



calcareous earth and alkali ; and the quantity was greatest 

 from tht infusion of" chestnut bark. 



The infusions were acted on by the acids and the pure 

 alkalis in a manner very similar to the infusion of galls. 

 With the solutions of carbonated alkalis they gave dense 

 fawn-coloured precipitates. They were copiously precipi- 

 tated by the solutions of limej of strontia^ and ofbarytes; 

 and, by lime water in excess, the infusions of oak and of 

 chestnut bark seemed to be deprived of the whole of the 

 vegetable matter they held in solution. 



By being boiled for some time with alumine, lime, and 

 magnesia, thcv became almost colourless, and lost their 

 power of acting upon gelatine ai:id the sails of iron. After 

 being heated with carbonate of lime and carbonate of mag- 

 nesia, they were found deeper coloured than before ; and, 

 though they had lost their power of acting on gelatine, 

 they still gave dense olive ^coloured precipitates -with the 

 salts of iron. 



In all these cases the earths gained tints of brown, more 

 or less intense-. 



When the compound of the astringent principles of the 

 infusion of oak bark with lime, procured by means of lime 

 water, was acted on by sulphuric acid,, a solution was ob- 

 tained, which precipitated gelatine, and contained a portion 

 of the vegetable principles and a certain quantity of sulphate 

 of lime ; a solid fawn-coloured matter was likewise formed, 

 which appeared to be sulphate of linie united to a little 

 taiinin and extractive matter *. 



The solutions were copiously precipitated by solution of 

 albumen. 



The precipitates they gave with gelatine were similar in 

 their appear-ance ; their colour at first was a light tinge of 

 brown, but they became very dark by exposure to the air. 

 Their composition- was very nearly similar; and, judging 

 froin the experiments on the quantity of gelatine employed 

 in forn>ing them, the compound of tannin and gelatine 

 from the strongest infusion- of oak bark seems to consist, 



■■' M. Mcrat GuiUot proposes a metlioJ of procuring pure tannin 

 (^Annalrs dr Chimu, tome x!i, p. 325), which consists in precipitating a 

 solution of un by lime waier. and' dccomprising it by nitric or muriatii: 

 acid. .The solution of the soUd rjiatter obtained in this way in iilcohhl 

 he considers as a solution of pure faimin ; but, from the experiments 

 above rnentioned, it appears that it must contain, besides tannin, some of 

 the extractive matter of the brak ; and it may likewise contain saline 

 matter, 



ia 



