Qy VEGETABLE ASTRINGENTS. n ] § 



colourless. To this filtered fluid jelly and the oximuriate 

 of tin were added without the slightest effect, and the oxi- 

 sulphate of iron only produced a blackish green tinge. In 

 this case it would appear, that the whose of the tan and the 

 extract, and the greatest part of the gallic acid were re- 

 moved by the antimony. In consequence of the readiness 

 with which the nitromuriate of gold parts with its oxigen, I Nitromuriate 

 thought of trying the effect of this reagent on the infusion £old, 

 of galls. Its first effect was to convert the brown colour of 

 the infusion into a dull blackish green, and after some time 

 a brown precipitate was thrown down in moderate quantity. 

 I was led by analogy to try the nitromuriate of platina ; the and of platina. 

 infusion was rendered instantly opake, and a reddish brown 

 precipitate was formed. 



These observations on the effect of the different reagents Constituents 

 upon the infusion of galls naturally lead to some conside- of lhes oluble 



. , . a i ■ i» ■ -. portion of 



rations respecting the constituents of the infusions, and also walls. 



©f the galls themselves. The soluble part of the gall-nut 

 is said to consist of four principal ingredients, tan, gallic 

 acid, extract, and mucus. The distinct existence of each 

 of these substances is supposed to be proved, either by our 

 being able to procure it in a separate state, cr by the em- 

 ployment of some tests which may recognize its presence. 

 To the tan and the gallic acid, both these methods of proof Tan and gallic 

 are, to a certain extent, applicable; they may, in some de-' aci ' 

 gree, be separated from the other parts of the galls, and we 

 are able to ascertain their presence by tests of the greatest 

 delicacy. There is reason to conclude, that, whenever jelly 

 throws down a precipitate from a vegetable infusion, tan is 

 present, and is the immediate cause of the effect ; although 

 it is probable, that it is not tan alone which unites itself to 

 the jelly. The existence of gallic acid is most distinctly 

 proved ; it may be obtained in a Ktate of almost perfect pu- 

 rity, and it may be detected by the oxisulpbate of iron in a 

 way that can scarcely be mistaken. But the proof of the Extract, 

 existence of extract is not so direct; it is confessed, that we 

 are unable to procure it separate from the other parts of the 

 galls, and therefore we are obliged to form our opinion, ei- 

 the r from the effect ©f tests, or from the observance of some 

 changes that the infusions undergo, which are thought not 



to 



