Light Absorption and Fluorescence. 21 



The values taken above of atomic frequencies *, infra-red 

 fundamental, and molecular phase frequency closely approxi- 

 mate to those observed with many compounds. It will be 

 seen that the amount of energy evolved in the complete 

 process may be very large, and for a « ram-molecule amounts 

 in the above instance to about 102,320 calories. It must, of 

 course, be remembered that in any reaction the observed 

 heat evolved is less than the total amount evolved in the 

 formation of the molecular systems of the products by the 

 amount necessary to resolve the initial substance or substances 

 into atoms. 



An important deduction from this molecular phase theory 

 may be made as re.-ards the energy changes involved in 

 chemical reaction. It is obvious that, in any reaction in 

 which the first stage is the resolution of the molecule into 

 its atoms, the energy necessary for this first sta<>e can at 

 once be found from the frequency of the phase in which that 

 molecule exists. Unfortunately, there does not seem to be 

 known at present a single instance of a simple reaction in 

 which the molecular phase frequencies have been accurately 

 measured both for the original substance and the products, 

 and consequently it is 7iot possible at the present time 

 accurately to calculate the net change of energy observed in 

 any reaction. On the other hand, in the vast majority of 

 chemical reactions the reacting molecules are not resolved 

 into their atoms in the first stage of the process. I have 

 shown in a number of cases that it is only necessary to 

 bring the molecules into a particular phase in order to enable 

 them to enter into the desired reaction. A very typical 

 example of the difference in reactivity shown by the different 

 molecular phases of the same molecule is afforded by benzal- 

 dehyde. In alcoholic solution this substance exhibits two 

 molecular frequencies in the ultra-violet, and therefore 

 two molecular phases co-exist. It is well known that in 

 alcoholic solution benzaldehydeis readily oxidized by gaseous 



* In the example given simple numbers have been used for the atomic 

 frequencies in order to avoid complexity in calculation. It is perhaps 

 worth while to point out here that there are certain indications that 

 the fundamental frequencies of the atoms of different elements are 

 possibly connected by simple arithmetical relations. A sufficient 

 number of these atomic frequencies has not yet been computed, owing; 

 to the dearth of accurate measurements of the subsidiary frequencies of 

 simple molecules, to justify any conclusions being- made. It is of some 

 interest, however, to note that in sulphur dioxide the oxygen frequency 

 24531 XlO 11 is almost exactly three times the sulphur frequency 

 8*19 xlO 10 , and that in the case of the water molecule the atomic fre- 

 quency 2-1159 x 10 u is very nearly twice the atomic frequency 

 10635x10". 



