even al liigliei' temperatures ; tlie mixture liowexer, was of a tairly 

 strong yellow colour. 



The other alcohols reduced the l)en/.opheiioiic in some sujin^' 

 spring days, with the exception of methylalcohol which recpiired a 

 much longer time. 



The research was then continued with allylalcohol, gej-aniol, cf/cio- 

 hexanol, benzylealcohol, [dienylinelhylalcohol, l»en/.hydrol and ciniia- 

 mylalcohol. Of these, the saturated alcohols reduced rapidly and 

 quantitatively ; the allylalcohol was attacked more slowly with form- 

 ation of acraldehyde (even after two months' exposure to light, the 

 acraldehyde was unchanged, thus showing that the light alone does 

 not exert a polymerising influence on this mobile substance). 



The geraniol was also oxidized very slowly, the cinnamylalcohol 

 remained unaffected (we will refer to this behaviour later). 



A few tertiary alcohols were also inxestigated ; it was expected 

 that these would remain unaffected and indeed this was the case 

 with the dimethylethylcarbinol after two months' exposure; during 

 that period, diaethylmethylcarbinol had generated 0,3 gram of pina- 

 eone ; with methyl-di-n-propylcarbinol the separation of pinacone 

 started after a few days and after tw^o mouths 0.7 gram had formed. 



From this we notice that when the chain becomes longer, the 

 activity of the hydrogen of tertiary alcohols gets eidianced, which 

 enables it, with the cooperation of sun-light, to attack an aromatic 

 ketone; what gets formed from the alcohol has not been investigated 

 by us. 



From observations of Ciamician and Silber^) it is known that the 

 hydrogen of some hydrocarbons, such as toluene, is already active 

 enongh to cause this reduction. We ha^'e been able to show that 

 also the hydrogen of the rijclohe.iuwe is transferred to the ketone, 

 on the other hand, hydrogen itself was not capable of acting. 



Besides benzophenone some other ketones — particularly those 

 that were previously sul)jected l)y us to the action of aluminium 

 amalgam — were subsecpiently exposed in alcoholic solution to 

 the light. 



Nothing i)ut pinacone was ever obtained, but the phenomena 

 occurring in these photo-reactions induced us to systematically repeat 

 a large part of these purely f|ualitati\ o obsei\ atioiis in such a manner 

 that on using a verv sim[)le modus oi^ii'vandi a relatively-quantitative 

 result was still obtained. 



1) B. 43. 1537 (1910). 



