.%5 



B. As soon, however, us ravs for the one ketone are also eon- 

 snmed by the otlier one. the quantity of pinacone will be less than 

 the sum in qnestion and, moreover, the proportions of concentrations 

 will no longer be a matter of indifference. 



For in the layer where the photo-reaction takes place each molecule 

 of the one ketone requii-es a i)art of the li*ilit-enei-g\v also wanted l\y 

 the second ketone, so that the liindrance experienced by the latter 

 will become greater when its relative concentration gets less. 



C. The extreme case would be that both ketones i-equire just 

 the same rays; we should then obtain a quantity of each of the 

 ketones which in equimolecular concentration is equal to half the 

 quantity that forms in the tube with the separate ketone (always 

 supposing that no other ol)stacles occur). 



The phenomena recorded by us are now best understood from 

 the su|)position B: a ketone does require specitic rays from its 

 neighbour. Some of the observations ap|n-oach to A. others to C, 

 some even exceed this extreme case, showing that the action is 

 more complicated than was at first supposed, as will appear from 

 the subjoined tabulated survey. 



TABLE XI. 



