Method of obtaining pure Tannin. J51 



upon Camplioric Acid*, in which he has treated of the converfion of camphor into oiU 

 Excepting this, nothing is faid upon the fubjedl by M. Prouft but what is already 

 univerfally known. 



In the fecond article, which is more interefting than the firft, he communicates fome 

 methods, more fimple than thofe which he had previoufly pointed out, of ohtaining pure 

 tannin, the principle of which he has obtained from the excellent Memoir of Citizen 

 Deyeux upon the Nut-gall. 



The procefs confifts in pouring a folution of carbonate of pot-afh into an infufion of 

 galls. By the mixture of thefe two liquids, a yellowifli white precipitate is formed, in 

 the form of a cogulum, which Ribaucourt took for an earthy and which it is only nectflary 

 to wafli with a little cold water to obtain the pure tanning matter. But care muft be takea 

 notto walh it with too much, nor with warm water; for however Ijttie foluble this matter 

 may be, it is neverthelefs enough fo, to difappear totally in a tderably large quantity of 

 water. Hence it follows, that in order to enfure complete fuccefs in the operation, the 

 infufion of galls muft not be too much diluted with water, finc.e in that cafe there will be 

 no precipitation. 



It is no lefs eflential that the alkali fliould be perfeftly faturated with the carbonic 

 acid, becaufe an excefs would favour the folution of a certain quantity of the tannin, 

 which would be greater in proportion as the alkali was more cauflic. Thus it is feen that 

 the tannin is feparated from its folution by an alkaline carbonate, not as mi^ht be fuppofed 

 by faturating the gallic acid but by engaging its water of folution ; for all the falts which 

 have a certain degree of affinity with 'tliis liquid in the cold produce the fame effeft. 



But however fmall the quantity of water that may be ufed, and whatever its temperature 

 may be, fome tannin always remains in folution ; becaufe it is foluble in a certain pro- 

 portion even of the coldeft water. The greateft part of this matter, which thus remains in 

 folution, may be obtained by evaporating any portion of the liquid, and part of the tannin 

 feparates by cooling, which is more or lefs in proportion to the quantity of water eva» 

 porated. The tannin, when it has been thus feparated from the other fubftances which 

 accompanied it in the galls, has the appearance of a glutinous paftcj of a yellowifh grey 

 colour, the parts of which adhere to each other in a confiderable degree. It dries with 

 difficulty •, but when it is fpread in thin layers upon earthen plates, and afterwards expofed 

 to the heat of a ftove, it fitft melts, then becomes dry, and at laft acquires the appearance of 

 a kind of yellow refin, with a vitreous fradure. This tannin, fubmitted to diftillation, 

 affords a faline liquid, in which the fmell of ammoniac is diftinguifhed, and which poffeffes 

 the property of blackening folutions of the red oxide of iron ; a property which muft be 

 attributed to a fmall quantity of tannin volatilized without alteration, and not to the gallic 

 acid, becaufe it does not afford a green colour with alkalis. 



• Philof. Journal,, II. 57. 



The 



