332 PHOTOSYNTHESIS 



wave length thus has its own energy and the shorter the wave lengths of 

 light, the larger are the units of energy as becomes evident from Table 40. 



TABLE 40 



Energy Corresponding to Various Wave Lengths of Light. 



Wave Lengths hv Q = N hv 



Color in \i\i ergs cal. 



Red 750-650 2.62-3.02 X lO"*" 37,800-43,630 



Orange 650-590 3.02-3.33 X 10"" 43.630-48,060 



Yellow 590-575 3.33-3.42 X 10"" 48,060-49,320 



Green 575-490 3.42-4.01 X 10"" 49,320-57,880 



Blue 490-455 4.01-4.32 X 10"" 57,880-62,330 



Violet 455-395 4.32-4.97 X 10"" 62,330-71,800 



Einstein's principle was deduced for an ideal, reversible, unimolecular 

 reaction of a gas or a dilute solution exposed to monochromatic radiation. 

 It has been found that in some cases the photochemical equivalent is less 

 than that demanded by theory and in other reactions it is many times 

 greater. 



Q . . 



The equation w = — is apparently not directly applicable to the photo- 



hv 

 synthetic reaction, for one quantum of the wave-length used in photosyn- 

 thesis is not sufficient to decompose one mole of carbon dioxide. Warburg 

 and Negelein therefore proposed the formula {k a proportionality factor) : 



n = k^ (1) 



hv 



The equation would indicate that the number of molecules of carbon 

 dioxide decomposed is proportional to the number of absorbed quanta, 

 and assumes that each quantum absorbed produces the same chemical re- 

 action. The proportional number of molecules of carbon dioxide decom- 

 posed by light of different wave lengths was thus calculated and k was 

 taken to indicate the number of molecules of carbon dioxide decomposed 



by one quantum or — the number of quanta necessary for the decomposi- 



tion of one molecule of carbon dioxide. Thus the following number of 

 quanta of different wave lengths have been calculated as required to 

 decompose equivalent quantities of carbon dioxide. This has been ob- 

 tained by dividing equation ( 1 ) by No, the Avagadro constant : 



No hv No 



or /t = 4>o • hv . No, where *o is expressed in — ;— - (mean values). 



cal. 



It is apparent from these results of Warburg and Negelein for the 



decomposition of one molecule of carbon dioxide that there are required 



about 4 quanta of red and yellow light and about 5 quanta of blue light. 



