234 SCIENCE PROGRESS. 



(33) on tautomerism. The aim of the work was to ascertain 

 the constitution of substances which might either contain 

 the group :CH'CO* or :C:C(OH)\ and also to find 

 whether a substance might not exist partly in the one form 

 and partly in the other, the relative amounts varying with 

 the temperature. It was found that ordinary fatty and 

 aromatic ketones, diacetyl, dipropionyl, and acetonylace- 

 tone, the alkyl derivatives of the acetoacetic esters, acetyl- 

 formic and acetylacetic acids are true keto-compounds. 

 The observations extended also to derivatives of campho- 

 carboxyllic, malonic, and ethyl-malonic acids, etc. 



In general, where the comparison is possible, the results 

 obtained for the constitution of the substances at ordinary 

 temperatures agree with those deduced by Perkin (34) from 

 his work on magnetic rotation. This is, however, not in 

 general the case as regards the effect of temperature. 

 Perkin found that all diketonic compounds of the fatty series 

 exist, partly at least, in the hydroxylic condition, and that 

 as the temperature rises gradual change into the ketonic 

 modification takes place. In the case of acetylacetone and 

 ethyl acetone oxalate, for example, Bruhl concludes on the 

 other hand that the constitution is independent of the 

 temperature. The methods which have up till now 

 been used in estimating this alteration consists in finding 

 whether the molecular refraction, dispersion, or magnetic 

 rotation varies with the temperature ; because these 

 constants are greater for unsaturated than for saturated 

 compounds. But even in the case of stable substances 

 the molecular refraction and magnetic rotation vary to some 

 extent with the temperature, hence their indications of 

 tautomeric change are always more or less uncertain. In 

 his paper Bruhl relies on the indications of dispersion alone, 

 as it is highly influenced by constitution, and for a stable 

 substance is little altered by the temperature. It is to be 

 hoped that a more minute study of the effect of temperature 

 on the optical constants of stable substances will serve to 

 explain the above discrepancy, and put upon a firm basis 

 what promises to be one of the most beautiful applications 

 of physical methods to chemical problems. 



