CONTRIBUTIONS FROM THE ROGERS LABORATORY 



OF PHYSICS, MASSACHUSETTS INSTITUTE 



OF TECHNOLOGY. 



LIV.— ON THE EQUILIBRIUM OF THE SYSTEM CONSIST- 

 ING OF CALCIUM CARBIDE, CALCIUM CYANAMIDE, 

 CARBON, AND NITROGEN. 



By M. de Kay Thompson and Robert H. Lombard. 1 



Presented by H. M. Goodwin, October 12, 1910. Received September 24, 1910. 



1. Introduction. 



Since the discovery by Frank and Caro ^ that pure nitrogen is ab- 

 sorbed by impure calcium carbide at high temperature, according to 

 the reversible reaction : 



CaCs + N2 :ii^ CaCNa + C, 



calcium carbide has been employed on a commercial scale for the fixa- 

 tion of atmospheric nitrogen. This method yields four times as much 

 nitrogen for a given amount of power as the direct oxidation in an 

 electric arc. Calcium cyanamide can be used directly as a fertilizer, or 

 it may be the starting point for the manufacture of other nitrogen 

 compounds. In consequence of the importance of this reaction, we 

 were led to undertake the determination of the equilibrium pressure of 

 the nitrogen in the above reaction for a number of different tempera- 

 tures. In this system there are three components, and four phases ; 

 consequently, according to the phase rule there will be one degree of 

 freedom ; or for every temperature, a corresponding pressure at which 

 equilibrium will exist. 



The method of carrying out this investigation was to heat a graphite 

 crucible containing graphite, calcium carbide, and calcium cyanamide, 

 in an Arsem vacuum furnace ^ in an atmosphere of nitrogen. The 



^ The following research was carried out under a grant from the Rumford 

 Fimd of the American Academy of Arts and Sciences. Grateful acknowledg- 

 ment is hereby made to the trustees of this fund. 



2 Z. f. angew. Chem., 19, 853 (1906). 



^ Trans. Am. Electroch. Soc, 9, 163 (1906). 



