21^ ON YEGETABLE ASTRINGENTS. 



from the infusion of galls*, but in the successive infusions, for 

 some time after they have ceased to act, jelly still continues 

 to prod vice a precipitate. Lime water has been proposed by 

 Mr. Merat-Guillot as the most commodious agent for sepa- 

 rating the tan from the other ingredients in the infusions, in 

 order to obtain it in a pure statef, and Mr. Murray seems 

 to regard it as the least exceptionable process^. . The alu- 



Alurninous minous salts, alum, the sulphate, and the muriate of alu- 

 mine, have been employed to denote the presence of extract 

 in the infusior>.-§ : but whether they act upon the tan or ex- 

 tract, they are much less delicate in their operation, than 

 either galls or the oxides of tin. By successively diluting 

 ^n infusion of a known strength, and examining it at differ 

 rent periods with jelly, the oximuriate of tin, and alum, 1 

 have always found the effect to cease first in the alum. Sul- 

 phate of alumine is rather more delicate than a saturated 

 solution of alum, while muriate of alumine seems to be 

 less 50. The most delicate and the most universal preeipi- 



Acetate of tant of vegetable infusions is the acetate of lead, which acts 



' equally upon all the constituents, the tap, the extract, and 



the gallic acid, and removes them completely from the fluid. 

 In the detection of the gallic acid it seems to exhibit even 

 more delicacy than the oxisulphate of iron. Mr. Vauque- 

 lin, in an elaborate and valuable paper on the effect of re- 

 agents on the different species of cinchona]|, employed the 



Tr.rtanzed an- tartarized antimony as one of his tests. I formed a satu- 

 rated solution of it in water, and observed its action on the 

 infusion of galls. The effect is very considerable, convert- 

 ing, as it were, the whole of the fluid into a pulpy mass ; the 

 precipitate subsides very slowly, but it is easily separated 

 by a filtre, and leaves the infusion perfectly transparent and 



* Deyeux, Ann. de Chim, XVII, 19. 



Proust, ibid. XXXV, 33. 



Although Mr. Deyeux first noticed th; action of the carbonated alkalis 

 upon tan, he does not appear to have attempted to procure it in a state of 

 purity by this process. 



f Ann. de thim. XII, 323. 



■\ ChemMtyJV, 275 



§ Davy, J'hil. Trans. 1803, p. 23?. 



|1 Ann, de Chim. LIX, 113. journal, vol. XIX, p. 1C6, 203 



colourless 



iimony. 



