853 



ketone concentration (in regard to the sensitive snbstance a reaction 

 of the order). 



By selectinji,- the alcohol itself as a solvent the change in con- 

 centration thereof conld be elirninaled. (Table 1). 



In order to determine the oi'der of the reaction in regard (o the 

 alcohol, benzene was chosen as being a general, non-absorbing and 

 non-redncing solvent. (Table \a) (Chronologically these last experiments 

 were made after tlie position of the active light in the spectrum 

 had been ascertained; we, however, state them here becanse thej 

 enabled ns to give a complete image of the course of the reaction.) 



We notice that this reaction is indeed independent of the con- 

 centration of the ketone, but not independent, however, of the con- 

 centration of the alcohol. As the rpianfities thereof had been chosen in 

 snch a manner that they were amply sufHcient even at the slightest 

 concentration, it follows from the tigiires ol)taine(l that the velocity 

 of the pinacone formation is pro])ortional to the concentration of 

 the alcohol. ') 



Thns we may represent the reaction by the kinetic equation : 



'^"^ = KL.[AlcoL\ 



With a constant light-quantity, t!ie velocity of the pinacone foima- 

 tion thus becomes proportional to the alcohol concentration ; how 

 many molecules of the ketone act simultaneously carinot be ascer- 

 tained in this manner. As, however, pinacone and aldehyde are 

 formed and as according to the above equation one molecule of 

 alcohol is attacked simultaneously, the reaction scheme becomes: 

 C,H,OH + 2(C,HJ,C0 = C\H,0 + (C,HJ,(C0H), •^). 



Tn order to learn the temperature coefticient the ordinary tubes 

 (16 mm. diameter) were enclosed and sealed into a second tube 

 (24mm. internal diameter); the intervening space was tilled with 

 conductivity water and now two of these tubes were exposed to 

 light as described, one of them being kept at 25°— 28° and the 

 other at 75°— 78°='). 



^] Here we have assumed that the change in concentration of the alcohol duiing 

 eacli of tlie I'our experiments was so slight that it. could be regarded as l)eing 

 constant; this, of course, is not coirect and we really ought to Jiave taken each 

 time a portion from larger apparatus. In that case, however, the experiments 

 would become much more complicated, l)ecause the liglit-quantily did not then 

 remain constant during the experiment, llencc, we have rested content with the 

 above niudas optrandi which is sufticiently accurate for our purpose. 



~) For a mixture of ketone and benzhydrole we have proved this reaction scheme 

 yet in another manner (see next communication). 



3) Compare R. Luther and F. Weigert, Z. phys, dh. 53, 400 (1905). 



