266 PROCEEDINGS OF THE AMERICAN ACADEMY. 



TABLE IV. 



Showing the Change in the Heat of sthe Reaction with the 

 Temperature. 



The value of j-- is of course constant for every temperature. 



The hne as drawn in Figure 5 seems to represent the observations 

 better than any other. The maximum variation in the slope would be 



dp 

 represented by the lines AB and CD. From the value of ~ obtained 



from these lines, the heat was calculated for 1200 degrees and found to 

 be 20,700 and 25,800 calories respectively. This shows that the value 

 calculated from the best representative line, 27,500, cannot be in error 

 by more than 2000 calories, or 7 per cent- 

 It seems evident from the fact that the heat effect is greater the 

 lower the temperature, that it would be advisable to work at as low a 

 temperature as possible in the fixation of nitrogen by this method, be- 

 cause less heat would be required from external sources. This would 

 be true if the velocity of the reaction did not decrease with decreasing 

 temperature, for this might more than balance the benefit due to the 

 increase in the heat of the reaction. 



In view of the enormous increase in the heat of the reaction with 

 decreasing temperature, as computed from these measurements, it is 

 desirable that the heat should be measured in some other way. This 

 might be done, as suggested by Mr. S. Peacock, by combustion experi- 

 ments in a bomb. This would give indirectly the heat of the reaction 

 at room temperature, which would be expected to be much larger than 

 the values calculated above. 



The free energy increase of the reaction 



CaCa + N2 ^ CaCNs + C 

 at 1450° C, taken from left to right is 



== — 4.57 X 1720 X 0.218 

 = — 1714 gram calories. 



At 1100° C, M^= - 6700 calories. 



