868 



explained in the above cited mannei\ There seems to l»e a connexion 

 here between the extent of the impediment and the non-appearance 

 of the photo-reduction. 



Now, in order to eliminate the hindrance wliich might eventually 

 take place owing to the mixing, the oft-qnoted jacketed tubes were 

 filled in such a manner that in the inner tube was aUvays inserted 

 a definite ketone and in the jacket diverse other ketones. 



The light then first traversed a ± 2 mm. thick layer of a ketone 

 then to exert its action on the benzophenone ; in this way we could 

 form a better opinion as to the absorption of rays of light by the 

 one ketone (in the jacket) which were needed for the other ketone 

 (in the inner tube). 



There exists no doubt that all ketones absoi'b actinic rays intended 

 for the benzophenone; the degree of this absorption is certainly 

 very different and specific. 



The ketones which were attacked in the jacket were, during the 

 experiment, reduced in concentration, so that the conditions for the 

 reducing of the benzophenoiie in the inner tube gradually became 

 more favourable; this causes, however, that we can only consider 

 as fairly comparable the expei-iments where no reduction lakes place 

 in the jacket. Hence, a few ketones have been placed in the jacket 

 in benzene solution whilst in the inner tube was again present a 

 solution of 2 grams of benzophenone iu 20 cc. of absolute alcohol; 

 the following result was thus obtained : 



TABLE XV. 



It appears that several ketones absorb rays of light which effect 

 the benzophenone activation, even when they are dissolved in 

 benzene. 



The reversible yellow coloration of this benzene solution, however, 

 tells us to be careful, foi' the activated ketone can form with benzene 



