270 PROCEEDINGS OF THE AMERICAN ACADEMY. 



would be changed to carbon monoxide which would decompose any car- 

 bide formed. The result of the experiment is, however, not conclusive. 

 Since calcium oxide was found in the white powder, an experiment 

 was carried out to see to what extent lime would distill when heated 

 alone in a vacuum. A graphite crucible was filled with pieces of 

 Merck's lime about the size of a pea, and was heated in a vacuum for 

 three hours at 1531 degrees. On opening the furnace it was found 

 covered on the inside with a thin greyish-white powder. On collecting 

 this it filled about one half inch of an ordinary test tube, and was 

 placed in a desiccator several days before testing. It was then dis- 

 solved in hydrochloric acid and tested for calcium with ammonia and 

 ammonium oxalate ; a large amount of precipitate of calcium oxalate was 

 formed. This experiment therefore shows that lime distills at about 

 1500 degrees in a vacuum. This doubtless is the cause of the thin layers 

 always found in the experiments on the equilibrium of the reaction 

 CaO + 3C :^ CaC2 + CO. It was not known at the time of the 

 determination of this equilibrium that lime is distilled in the neighbor- 

 hood of 1500 degrees.^ 



3. Summary. 



The equilibrium pressure of nitrogen in the reaction 



CaCa + N2 ^ CaCNa + C 



was determined from both sides for a number of temperatures between 

 1050° C. and 1450° C. The results are plotted in Figure 5. It was 

 found that the heat of the reaction varies enormously with the tem- 

 perature. The values calculated from the plot in Figure 5 are given 

 in Table IV. 



The free energy increase of the reaction taken from left to right is 

 -1714 gram calories at 1450° C. and -6700 calories at 1100° C. 



Calcium cyanamide distills the cold parts of the vacuum furnace at 

 temperatures as low as 1050° C. Pure lime distills appreciably in the 

 neighborhood of 1500° C. 



Electrochemical Laboratory, Rogers Laboratory of Physics, 

 Massachusetts Institute of Technology, 

 Boston, Mass., September 23, 1910. 



' These Proceedings, 45, 449 (1910). 



