Intelligence and Miscellaneous Articles. 323 



acid (S-f-S) but two atoms of sulphuric acid united to an atom of 

 sulphurous acid (2S-f-S), which by calculation gives in a hundred 



P arts Sulphurous acid 28-58 



Sulphuric acid 71*42 



100-00 



As the sulphurous acid is that which exists in the least proportion 

 in this combination, it may be considered as the basic constituent, 

 and in this point of view the compound is a neutral sulphate(bi-sul- 

 phate ?) in which the sulphuric acid contains thrice as much oxygen 

 as the base. — Journal de Pharmacie, March 1837. 



ON GALLIC ACID. BY M. ROBIQUET. 



M. Robiquet remarks that before M. Pelouze had published his 

 work on tannin and gallic acid, it was generally admitted that the 

 acid was ready formed in the gall nut, and it was far from being 

 supposed, as attempted to be shown by this chemist, that gallic acid 

 was entirely derived from the tannin. M. Robiquet, after stating 

 some difficulties in admitting this opinion, observes, that whether 

 the acid pre-exists or not in the gall nut, it is certain that a large 

 quantity separates independently of contact with the air or with 

 oxygen, and without any action, if indeed there be one, which 

 occasions the evolution of any gas. 



M. Robiquet then details experiments which show that tannin 

 does not yield much above half its weight of gallic acid ; and he 

 observes that there is great disproportion between the time required 

 to convert pure tannin into gallic acid and that required for the en- 

 tire gall nut. In the latter case a month is sufficient in favourable 

 weather to complete the action. He is therefore of opinion that 

 the gall nut contains other principles, which facilitate the operation 

 by acting as a kind of ferment, and M. Robiquet supposes that the 

 gum, or rather mucilage, which may be separated by water from the 

 residue after the action of aether upon the gall nut, performs this 

 office. 



Following out the opinion formerly stated by M. Chevreul, that 

 tannin may be a compound of which gallic acid is one of the ele- 

 ments, M. Robiquet examined whether this idea was probable, and 

 the results were the following : M. Pelouze had inferred from his 

 analysis of tannin that it consisted of C 18 H 18 O 12 . M.Liebig has 

 since remarked that the analysis agrees better with C 18 H 16 O i2 , and 

 preferred the latter as more easily explaining the conversion of tan- 

 nin into gallic acid. M. Pelouze nevertheless retained the first for- 

 mula, and M. Robiquet adopts it as agreeing better with his new view 

 of the subject. Thus, this formula C l8 H 18 0» 2 ==* (C? H 6 O + H* O) 

 + H 2 C 4 represents 2 atoms of crystallized gallic acid, plus 1 atom 

 of a carburetted hydrogen of the same composition as benzin. The 

 formula adopted by M. Liebig will equally apply to other changes. 

 Thus, the 3 atoms of tannin are equivalent to 6 atoms of gallic acid, 

 plus 2 atoms of dry pyrogallic acid, 3 (C 18 H 1<5 12 )= O 4 H 48 36 = 

 6 (C? H 6 O*) + 2 (C 6 H 6 O) ; or still better, by admitting that tan- 



2T2 



