JflSTORY OF THE GALLIC ACID, 69 



If one of the gallats, that of soda for instance, be treated with Gallats treated 

 charcoal,the tannin will be entirely destroyed, so that the solution 

 will no longer precipitate glue; and after repeated boiling with 

 fresh portions of charcoal, it will no longer act on sulpljat of iron. 



The liquor being afterward evaporated to dryness, and distil- stin S lve acetic 

 led with very weak sulphuric acid, we still obtain acetic acid. 



I shall not insist any farther on the possibility of obtaining 

 acetic acid by decomposing gallic acid. I might mention the 

 experiments, which would tend to support the preceding, but 

 entering too minutely into these particulars would add nothing 

 to the facts I have already adduced. 



I shall conclude with an experiment, which appears to me Examination 

 important. The object was, to establish the nature of the elastic ° oducedljy 

 fluids resulting from the complete decomposition of the gallic decomposing 

 acid by heat. Mr, Deycux has announced, that he obtained 

 pnly oxigen gas, and carbon. Mr. Berthollct, who repeated the 

 experiment, says, that he had no oxigen gas, but constantly car- 

 bonic acid. 



These results, of which no other vegetable acid furnishes an 

 example, could not avoid exciting the attention of chemists. 

 In fact it is difficult not to admit hidrogen in the composition 

 of gallic acid; and Mr. Fourcroy has expressed his doubts on 

 this subject in his System of Chemical Knowledge, but the 

 question is not yet decided by experiment. 



In consequence I heated gallic acid in a retort. The fire 

 was gradually raised till the retort was red hot. During this, ac- 

 tion of caloric I obtained several jars full of elastic fluid. The The first por- 

 first contained only atmospheric air; the others carbonic acid t ™ e ret ^ 7 a f_ 

 gas: at least the gas had all the characters of thin acid; but tenwurd carbo- 

 the phenomena that occurred during the decomposition of the 

 gallic acid led mc to suspect, that, if any hidrogen gas had been 

 evolved, it could exist only in a very small quantity, I did not 

 satisfy myself therefore with the trial by limewater, and the ex- 

 tinction of a taper in the gas. Having perceived, that hidrogen mived with 

 gas mixed with.agreat deal of carbonic acid gas cannot be fried, y^."^^ 6 

 because this acid acts too promptly on the flame of the taper, 

 I passed a little caustic potash into the last jar of gas; agitated 

 }t, absorb the carbonic acid ; and then immersed a taper in the 

 residual gas, which burnt with flame, and thus afforded me. a 

 proof of the presence of carburetted hidrogen. 



The 



