TAUTOMERISM 131 



towards ferric chloride. The phenomenon was more striking 

 in ethyl-alcoholic solution : 



0-85906 after 10 minutes. 



0-85963 i^ hours. 



0-86072 20 



0-86066 ,, 8 days. 



In chloroform this was not observed : 



1.42277 after 10 minutes. 



1-42273 4 hours. 



It is questionable, however, whether in alcoholic solution 

 the process 



C 6 H 10 O 3 + C 2 H 6 O = aCH 3 C0 2 C 2 H 5 



did not occur. 



Whilst, therefore, the latest information points to a 

 tautomeric compound being a mixture in equilibrium of 

 two isomers, it may be remarked l that such a phenomenon 

 is only possible in a liquid or solution. In the solid state 

 one or other compound must be the stable form, and the 

 two can only coexist at the transition temperature. Liquid 

 or dissolved, however, the condition of equilibrium is 

 subject to gradual displacement with temperature, so that 

 a mixture in equilibrium is possible over a considerable 

 interval of temperature. In general, therefore, a solution 

 of a pair of isomers near the transition point would behave 

 as tautomeric. 



Here we may add the remark that the phenomenon of 

 tautomerism, like any other depending on atomic move- 

 ments, must vanish at the absolute zero. This, however, 

 is only in accordance with the known fact that tautomerism 

 does not occur in the solid state. Long before the absolute 

 zero all tautomeric compounds would become solid. 



1 Knorr, Berl Ber. 30.2389. 



I 2 



