THOMPSON AND LOMBARD, — NITROGEN IN CALCIUM CYANAMIDE. 267 



The errors in the temperature measurements are probably the main 

 cause of the deviations of the single determinations from the best rep- 

 resentative line. If all the error is assumed due to the temperature 

 measurements, the average deviation of a single point from the line 

 is only 12 degrees, and the largest deviation is 19 degrees. These 

 are not greater than the experimental errors in the temperature 

 measurements. 



The thermo-electric couple had been cut off several times since the 

 original calibration. It was subsequently calibrated as follows : 



TABLE V. 



Date. Temperature. ^, ?^™r°^*t„ n • ^fr°]\^ ""l 



'^ at Date given. Original Calibration. 



July 2 Sulphur point 3.60 3.60 



August 13 Copper point 10.08 10.19 



The original calibration had therefore remained practically constant 

 throughout the experiments. 



After each experiment for determining the equilibrium pressure, the 

 furnace walls were covered inside with a white powder. A similar re- 

 sult was obtained in determining the equilibrium of the reaction 

 CaO -f 3C :i± CaC2 + CO.^ It was noticeable, however, that there 

 was more powder formed with calcium cyanamide for a given tempera- 

 ture and given duration of heating than with calcium carbide. It 

 seemed probable that calcium cyanamide is volatile, especially after it 

 was found that the white powder gave a yellow precipitate of silver 

 cyanamide on adding silver nitrate to an ammoniacal solution of the 

 powder. It was therefore thought desirable to make an analysis of 

 this material. 



Some of the pure white powder was analyzed for nitrogen by the 

 Kjeldahl method, taking about one gram for analysis. The digestion 

 with chemically pure sulphuric acid was continued for five hours near 

 the boiling point ; immediately after, potassium permanganate was 

 added. The two determinations gave 12.38 and 11.67 per cent nitro- 

 gen, corresponding to 34.3 per cent calcium cyanamide. 



To get a check on this value, the calcium cyanamide was determined 

 by the method of Perotti.^ This method consists in allowing the 

 substance to stand over night in water, filtering and washing, add- 

 ing ammonia, and then an excess of silver nitrate. A yellow pre- 

 cipitate of silver cyanamide is produced which is filtered off, and the 



* Trans. Am. Electroch. Soc, 15, 197 (1909). 

 « Chemisches Centralblatt, 2, 1059 (1905). 



