248 FREE ENERGY OF BIOLOGICAL PROCESSES 



specialization, it would be too much to expect biologists to possess 

 this knowledge in addition to the mastery of their own special field. 

 They are, however, wilKng to cooperate with physical chemists to 

 bring about the desired progress in biological science. Unfortu- 

 nately, whenever they present their problems to the physical chemist, 

 they are always met with the statement: "Biological processes are 

 so highly complex that they are not susceptible to thermodynamic 

 treatment." 



Biologists and agriculturists cannot, of course, get satisfactory 

 information on this subject from text-books on physical chemistry, 

 since these embody principally the views and guesses of physical 

 chemists of past generations and are interesting from an historical 

 standpoint only. In fact, it was only within recent years that the 

 first serious attempt was made to base even chemical calculations 

 systematically on thermodynamic principles. This was done by 

 Lewis,^ and Lewis and Gibson.^ It is hoped that by the use of their 

 methods we may be able to do for general physiology, in a measure at 

 least, what Lewis has done for general chemistry. 



In order to find the maximum or free energy of any chemical proc- 

 ess, such as the transformation of mannite into carbon dioxide and 

 water, which certain bacteria utilize for the work required in decom- 

 posing sulfates, phosphates, nitrates, or in the "fixing" of nitrogen, 

 we must know not only the change in the heat content attending the 

 process, but also the change in entropy from the absolute zero up to 

 the given temperature, T, at which the process takes place. We 

 can then calculate the free energy of the process with the aid of the 

 thermodynamic equation 



AF = AH - TAS (1) 



where AF denotes the free energy charged, AH the change in heat 

 content, and AS the change in entropy of the isothermal process in 

 question. 



The thermochemical data found in the literature, although very 

 extensive, are, with few exceptions, extremely inaccurate, while the 

 measurements of usable entropies have only recently been started 



^ Lewis, G. N., /. Am. Chem. Soc, 1913, xxxv, 1. 



2 Lewis, G. N., and Gibson, G. E., /. Am. Chem. Soc, 1917, xxxix, 2554. 



