32 Tacts for a History of the Gallic Aclct. 



proofs ill confirniation of its presence; and to demonstrate 

 that this acid, combined with other substances, constitute* 

 the gallic acid. 



With ihis view I formed gallates of lime, barytes, potash, 

 and soda. These neutral coniiii nations afforded a violet red 

 colour with a solution of sulphate of iron, and scarcely pre- 

 cipitated glue, while the acid employed had the property of 

 forming with it a copious precipitate. On these salts, dried, 

 I poured some very weak sulphuric acid ; I distilled theuj 

 \\'\\\\ a gentle heat, and I always obtained acetic acid. 



The retorts contained a very deep brown matter. I cry- 

 stallized the salts that were perceptible of it, and obtained 

 sulphates. 



The supernatant mother-water had the properly of slightly 

 brownin"" the solution of sulphate of iron ; but this apjvcar- 

 ance does not prove the presence of gallic acid, for the black 

 colour of the mother-water was sufficient to give it this hue. 



If one of the gallates, that of soda for instance, be treated 

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

 the solution will no longer precipitate glue; and after re- 

 peated boiling with fresh portions of charcoal, it will no 

 longer act on sulphate of iron. 



The liquor being afterward evaporated to dryness, and di- 

 stilled with very weak sulphuric acid, we still obtain acetic 

 acid. 



I shall not insist any further on the possibility of obtain- 

 ing acetic acid by decomposing gallic acid. I might men- 

 tion the experiments which would tend to support the pre- 

 ceding, but entering too minutely into these particulars 

 would add nothing to the facts I have already adduced. 



I shall conclude with an experiment Vv'htch appears to me 

 important. The object wa'^, to establish the nature of the 

 elastic iluids resulting from the complete decomposition of 

 the gallic acid by heat. M. Deyeux has announced that 

 he obtained only oxygen gas and carbon. JM. Bcrthollet, 

 who repeated the experiment, says that he had no oxygeii 

 gas, but consti.ntly carbonic acid. 



These results, of which no other vegetable acid furnishes 

 an example, could not avoid exciting the attention of che- 



miiits.. 



