THOMPSON AND LOMBARD. — NITROGEN IN CALCIUM CYANAMIDE. 251 



a graphite lid with a hole in it, and then placed in the furnace. The 

 furnace was pumped out and the charge heated to a temperature at 

 which the experiment was to be made (or higher) until all gases were 

 driven off. Nitrogen, made by the Linde process and 90 per cent 

 pure, was let into the furnace after passing it over hot copper, soda, 

 lime, and phosphorous pentoxide. After allowing the nitrogen to enter 

 the furnace until the pressure was 2 or 3 centimeters, it was pumped 



1000 



950 



4 u 



2" 



I" r 



Distance from Surface of Block 



Figure 3. Temperature in Heraeus furnace at different distances from 

 the surface of carbon blocli used for calibrating the Wanner pyrometer. The 

 surface faced the pyrometer towards the left, in the figure. 



out to about 1 or 2 millimeters. This was repeated once or twice to 

 remove all other gases. The furnace was then filled with nitrogen to 

 a pressure that was certainly greater than the equilibrium pressure. 

 The furnace was usually hot when filled. The furnace was frequently 

 filled in the afternoon and the run started the following morning. On 

 heating with an excess of nitrogen some of it would be absorbed, pro- 

 ducing calcium cyanamide and carbon from the carbide, so that all 

 three solid phases were then present. After equilibrium had been 

 reached from this side, nitrogen was pumped out, and the equilibrium 

 was approached from the other side. The mean of the two results 

 was taken as the best value of the equilibrium obtainable. 



2. Experimental Data. 



A Siemens and Halske milli voltmeter of 471 ohms resistance was 

 used for measuring the temperature with a platinum platinum-rhodium 

 junction. The milli voltmeter was calibrated and the following table 

 contains the corrected value of the scale reading with the corresponding 

 temperature. 



