294 Facts for a Historij of the Gallic Acid. 



upon the red oxide of mercury; it instantly became brown, 

 and afterwards changed to black : the liquor then assumed 

 a deep brown colour : in this state it was still acid, gave a 

 blue colour to a S(^lution of sulphate of iron, and precipitated 

 glue; but it did not contain mercury. 



I boiled this liquor over a new quantity of oxide ; it then 

 became clear, without colour, and did not contain either 

 tannin or gallic acid. 



A part of the oxide of mercury was reduced ; the other 

 was mixed with concrete phosphoric acid, but nothing was 

 sublimed by the action of caloric. 



If we use charcoal previously purified in place of red oxide 

 of mercury, the solution of gallic acid loses almost entirely 

 its colour and taste ; ihe liquor becomes green, and does nut 

 precipitate ghie; but it still gives a violet blueish lint to the 

 solution of sulphate of iron. When boiled with a new quan- 

 tity of charcoal the liquid becomi'S colourless, and produces 

 no change in the solutions of glue and sulphate of iron. 

 After having evaporated it to dryness, there remained in the 

 capsule a brown substance, which precipitated the acetate 

 of lead in a dirty gray colour, and the nitrate of mercury 

 and muriatp of tin in yellow ; we may therefore consider it 

 as being an extractive matter. 



These experiments demoristrate that there exists no other 

 process for purifying the gallic acid of Scheele, except sub- 

 limation ; at least, that the proportions of oxide of tin em- 

 ployed by M . Berlhollet, but which he has not pointed out, 

 have not a great influence upon the result. The method of 

 purifying it by sublimation, however, cannot be admitted 

 if we wish to preserve all its properties. The different cha- 

 racters presented by these acids furnish the proof of this 

 assertion. 



Comparison of the Gallic, CrystaUixed, and Sublimed Acids, 



Crystallized yield of Scheele. 

 This acid gives to water a slight lemon colour; the solu- 

 tion becomes darker on the contact of the air ; it reddens 

 turnsole tincture : ilujc v.ater produces a blue colour in it ; 



am 



