GEORGE A. LINHART 251 



This would be the maximum amount of energy at the disposal of 

 the Azotohacter in 10,182.1 gm. of solution, 182.1 gm. of which is 

 mannite, if the latter were all converted into CO2. To be sure, a 

 certain amount of the carbon of the mannite is utilized by the bac- 

 teria in the building of their proteins; the exact amount so combined 

 will need to be determined experimentally. For the present, let us 

 assume that all the carbon in the mannite is converted into CO2. 



As previously noted in the introduction, a thermodynamical cal- 

 culation of transfer of energy involves a knowledge of the initial and 

 final states of the system. In the present instance, we have mannite 

 as the initial state — the final state is not yet known. For the purpose 

 of this calculation, we may assume the final product to be hydrated 

 ammonia. Under this assumption, — 740,600 calories would be suffi- 

 cient energy to form about 10 mols of ammonia from water and nitro- 

 gen gas; that is, if the bacteria acted directly or indirectly merely as 

 catalytic agents. As a matter of fact, it is shown in Greaves'^ sum- 

 mary of nitrogen fixation by Azotohacter that the amount of nitrogen 

 fijfed is only about 1 per cent of the weight of mannite, or, in molal 

 proportions, for every mol of mannite used up only about 0.1 

 mol of ammonia is formed. According to the source above quoted,, 

 we would obtain about 0.1 mol of ammonia instead of 10 mols, or 

 only about 1 per cent of the total available energy is utilized in the 

 fixation of nitrogen. 



* Greaves, J. E., Soil Science, 1918, vi, 181. 



