Dr. Turner's Notice on Oxalic Acid. 349 



of water, is decomposed by heat at a lower temperature than 

 the same acid after two equivalents of water have been re- 

 moved. Thus, on operating with the fully hydrated acid in 

 the same manner as with that which had fully effloresced on 

 the sand-bath, fusion took place at 209°, as stated by M. 

 Gay-Lussac, and not at 220° as 1 had found in heating some 

 crystals, which must previously have lost a little of their water 

 of crystallization. As the temperature of the bath rose to 

 230°, the fused mass remained quite tranquil, yielding a little 

 water, but not a particle of gas. At 240° there was still 

 scarcely any gas, and very little at 250° or 270°. Even at 

 290°, though there was violent ebullition from the rapid 

 escape of aqueous vapour, yet the evolution of gas was by no 

 means abundant: it became free at 310°, and was i-apid at 

 320°. In a second careful experiment the results were pre- 

 cisely similar. It is therefore apparent that oxalic acid, as 

 deposited in crystals fi'om solution, is decomposed at a consi- 

 derably lower tempei*ature than when it contains only one 

 equivalent of water. 



My observation on the decomposition of oxalic acid by sul- 

 phuric acid induces me to dissent from the explanation which 

 M. Gay-Lussac has suggested. Sublimed oxalic acid, acted 

 on by a considerable quantity of strong sulphuric acid, began 

 to effervesce by being kept for a few minutes in a vessel of 

 boiling water. The action indeed was slow, but it was per- 

 fectly distinct and continuous, the disengaged gas consisting 

 as usual of equal measures of carbonic oxide and carbonic 

 acid. The effervescence was much more free at 220°, and 

 still more so at 230° ; and yet the same acid, exposed to mere 

 heat, would not have yielded a particle of gas at the tempera- 

 ture of 330°. Oxalic acid, in its most hydrated state, if mixed 

 with a large excess of sulphuric acid, is decomposed at nearly 

 the same temperature as it is after having lost two-thirds of its 

 water, effervescing with moderate freedom at 220° ; whei-eas 

 it may be heated by itself to 230° without decomposition. 

 As the temperature in all these experiments was ascertained 

 by the same thermometer, they are quite independent of any 

 error in graduation. Such an error, which nuist be slight if 

 it exist at all, cannot account for the comparative results ob- 

 tained in my own experiments, thougli it may in part explain 

 the discordance in the observations of M. Gay-Lussac and 

 myself. It may surely therefore be inferred, that the decom- 

 position is not due to the sole agency of heat; and we may, 

 I apprehend, continue to explain tiie phenomenon on the 

 principle which has l)een hitherto generally admitted. 



1 concur with M. Gay-Lussac respecting the composition 



of 



