Intelligence and Miscellaneous Articles, 38 1 



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ON THE CONSTITUTION OF SOME ORGANIC ACIDS. BY M.DUMAS 

 AND M. LTEBIG. 

 Citric Acid. — Gay-Lussac and Thenard have analysed citrate of 

 lead. Berzelius has since determined the composition of citric acid, 

 citrate of lead, and fixed the constitution of this acid in a manner 

 which seemed definitive. However, from researches since made by 

 Berzelius, he has found that citric acid, being considered as com- 

 posed of C" H* O*, as was at first admitted, produced salts possess- 

 ing very extraordinary properties. Citrates of soda and baryta heated 

 to the temperature of 200*^ C. lose water which they do not contain. 

 The acid therefore appears to be decomposed. However if water 

 is added to these salts, the ordinary citric acid reappears with 

 all its properties. This mobility of the elements of citric acid has 

 engaged the attention of chemists. We have found that by using 

 certain precautions, the same quantity of water may be driven off 

 from many other citrates as well as from the citrates of soda and 

 baryta. It must be therefore admitted that this water does not 

 really form a part of the constitution of citric acid. This point esta- 

 blished, another difiiculty remains to be solved, which is, that, in 

 both Berzelius's experiments and in ours, each equivalent of citric 

 acid lost one third of an equivalent of water only, and no more. 

 This difficulty could not be overcome in the former opinions enter- 

 tained of the nature of acids, but in supposing the equivalents of 

 citric acid to be tripled, so that in the neutral citrates there would be 

 three equivalents of base, which may be represented as follows : 



C24 Hio O'l, real acid. 



C^^HioQii, 3H'^0 dry acid. 



C2^ H'o Oi», 3 H« O, 2 H2 O crystalUzed acid. 



C24 Hio Oil, 3NaOl 



3 Ba O l- real citrates. 

 3AgOj 

 Tartaric Acid,—T\iQ admitted formula for this acid cannot be made 

 to agree with the results obtained. According to Berzelius this acid 

 is represented by C H* 0\ M. Dumas says this analysis is not 

 doubtful in itself; but we have reasons for thinking that tartaric 

 acid is capable, like citric acid, of losing water, formed at the ex- 

 pense of its elements. To verify this, we have submitted tartar 

 emetic to a number of analyses, and are convinced that it loses two 

 equivalents of water, which it does not contain. Therefore every 

 equivalent of acid entering into the composition of tartar emetic 

 loses one equivalent of water. Instead of representing dry tartar 



emetic by C'^, H^, O'o, KO, Sb^ O^ 



it must be represented by C'^, HS 0^ KO, Sb^ O^ 2 H^ O. 



These two equivalents are driven olF at 220*^ Centigrade, and are 

 independent of the water of crystallization of the tartar emetic. 

 Other Acids, — Meconic and cyanuric acid present analogous phse- 



