HISTORY 0£ THE GALLIC ACID. 03 



Va repeat his experiments, and determine the nature of the results 

 that might arise from them. With this view I poured a solution With red oxide 

 of gallic acid or red oxide of mercury; which immediately °- fmerCLU 'y* 

 became brown, and gradually changed to black. The solution 

 too acquired a deep brown tint. In this state it was still acid, 

 gave a blue colour to a solution of sulphat of iron, and precipi- 

 tated glue; but it contained no mercury. 



I boiled this liquor on a fresh quantity of oxide; when it 

 became clear, colourless, and no longer contained either tannin 

 or gallic acid. 



Pari of the oxide of mercury Was reduced : the rest was mix- 

 •^1 with concrete phosphoric acid [so the original], but nothing 

 was sublimed from it by the action of lead. 



If charcoal previously purified be employed instead of rod With charcoal, 

 oxide of mercury, the solution of gallic acid loses almost entirely 

 its taste and colour ; the liquor becomes green, and no longer 

 precipitates glue; but it still gives a violet blue tint to solution 

 of sulphat o{ iron. Boiled with a fresh quantity of charcoal, 

 the liquid becomes colourless, and no longer produces, any 

 change in the solution of glue or of sulphat of iron. After it is 

 evaporated to dryness, a brown matter remains in the capsule* 

 which precipitates acetat of lead of a dirty gray, .and nitrat of 

 mercury and muriat of tin yellow; sq that we may consider it 

 as extractive matter. 



These experiments prove, that there exists no process for Only robe 



purifying Scheele's callic acid but sublimation : unless the pro- P urihe(1 b / 

 r J ° ? l sublimation,' 



portion of oxide of tin employed by Mr. Berthollet, which 



he does not mention, has a great influence on the result. Yet 



the mode of purifying the gallic acid by-sublimation cannot be 



adopted, if we wish it to retain all its properties. The different but tins altera 



characters exhibited by the two acids will afford proofs of this 1 s P ro P-j ie • 



assertion. 



Co?nparison of the crystallized and sublimed Gallic Acids. 



Sckecle's crystallized acid imparts to water a slight lercon CO* Solution of the 



lour: this solution grows deeper coloured by the action of the ^J^ a 



air: it reddens tincture of litmus: limevvater produces in it a 



blue colour, which changes to that of peach blossoms lithe lime- 



. . - ' » »• ,-i p •. • • i ^ with lime 



water be in excess, and on adding a tew drops of nitric acid to M , ater 



a rose colour. The same phenomena take place with water of barytes, 



•f barytes. This 



