453 



vessel descends below the crilioal. In the region of maximum acti- 

 vation all the photo active light is, theietbre, arrested by a layer 

 of J nun., and this takes place independent of the solvent used. 

 These phenomena are in perfect harmony with what was found 

 before in the ketone reduction. Corresponding experiments with 

 diacelyl and benzoyl acetyl lead to perfectly the same results. 



I. benzophenon \ 



II. phenylcyciohexyl ketone / Fig. 5. 



III. phenyl, n. hexyl ketone ' 



III. , , 



IV. acetophenon 



V. acetylbenzoyl 



VI. diacetyl 



t^ig- 



cone, in mol. 



Fig. 5. 



cone, in niol. 



Fig. 6. 



h. For the photo-activity of the mono-ketones the "aromatic", 



character is in general decisive '), constitutive factors being of 



influence by the side of it. Thus the photo-activity of benzophenon 



has been reduced to about half its value, when one of the nuclei 



») Cohen, Ghem. Weekbl. la, 902 (1916). 



