48 



SECTIONAL ADDRESSES. 



activated by irradiation with white light for 18 hours. The powder must 

 be used very soon after it has been activated. 



In fig. 3 is shown the relation between the temperature and the yield, 

 and it may be seen to be linear between 5° and 31°. This result is of some 

 interest in view of the fact that pure photochemical reactions have a 

 temperature coefficient of unity. 



In seeking for an explanation of the temperature coefficient it is- 

 necessary to review all the known facts. It has previously been shown that 



1 . Carbonic acid in aqueous solution is not acted on by white light ; • 



2. Carbonic acid when adsorbed on a coloured surface does not react 

 in the dark ; 



3. Carbonic acid when adsorbed on a coloured surface and irradiated 

 by white light reacts to give carbohydrates. 



0-08 



0-07 



006 

 Q 

 ui 005 



004 

 003 



002 



01 



/__ 



'' ' I I I I \ 



8 12 16 20 2^ 28 32 36 ^0 44 48 



TEMPERATURE °n 

 Fig. 3. 



It follows as a necessary conclusion from the facts that the complete 

 activation of the carbonic acid must take place in two stages, namely, 

 partial activation by adsorption with the formation of a molecular state 

 capable of absorbing some rays within the visible spectrum, whereby 

 the activation is completed by photochemical means. Furthermore, the 

 number of partially activated molecules which are able to enter into the 

 final reaction is in linear proportion to the temperature. It is this first 

 stage of partial activation which is of interest in our quest, since it is 

 evident that the adsorption process alone is not sufficient to bring the 

 molecules into a state which enables them to react photochemically under 

 the influence of visible light, the supply of heat energy being necessary to 

 add the finishing touch to the partial activation. 



