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XLIII. Notice on Oxalic Acid. By Edward Turner, M.D. 



F.R.S. L. Sf E. Sfc, Professor of Chemistry in the University 



of London*. 

 TN a former Number of this Journal + I had occasion to 

 ■*■ publish some remarks on the volatility of oxalic acid ; and 

 about the same time M. Gay-Lussac published in the Annates 

 de Ckimie et de Physique, vol. xlvi. p. 218, a short memoir on 

 the easy decomposition of oxalic acid by the agency of heat J. 

 In my notice the sublimed acid is described as supporting a 

 temperature of 330° Fahrenheit, without any decomposition ; 

 while M. Gay-Lussac, speaking of the crystals in their ordi- 

 nai'y state, describes them as being decomposed at so low a 

 temperature as 230° Fahrenheit. As these statements may 

 be thought contradictory, while at the same time a correct 

 knowledge of these facts is required for understanding an in- 

 teresting point of theory, — the action of the sulphuric on oxalic 

 acid, — 1 have re-examined the subject with the hope of cor- 

 recting any inadvertence which may have been committed. 



In the experiments which I have made with this view, the 

 heat was applied through the medium of a small mercurial 

 bath, heated by a lamp: the acid to be decomposed was con- 

 tained in a small glass tube, the sealed end of which was 

 plunged into the bath, and its other extremity connected in 

 the usual manner with a mercurial trough. The tempera- 

 ture was ascertained by fixing the bulb of a thermometer in 

 the bath during the whole continuance of the experiments. 

 By operating in this way I found that my former statement 

 was strictly correct. Oxalic acid containing only one equi- 

 valent of water, whether prepared by merely heating the or- 

 dinai-y crystals or by sublimation, sustained a temperature of 

 330° without yielding either water or gas. As the thermo- 

 meter rose from 330° to 31'0°, gas began slowly to appear, and 

 at 370° it was freely disengaged. It hence follows that the 

 best temperature for subliming oxalic acid is 330°: it then 

 sublimes with rapidity, and yet there is no loss by decomposi- 

 tion ; but before exposure to this degree of heat, the acid 

 should previously be dried as much as possible at a lower 

 temperature. 



But it does not necessarily follow, because my statement is 

 correct, that that of M. Gay-Lussac should be erroneous. On 

 the contrary, though we differ as to the precise degree of heat 

 at which decomposition takes place, I find that crystallized 

 oxalic acid, containing one equivalent of real acid and three 



* Coninmnicated by the Author. 

 t Phil. Mag. and Annals, N.S. vol. i.\. p. 161. 

 [i Sec also Phil. Mag. and Annals, vol. x. p. 153.— Edit.] 



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