128 C. H. Warren — Calcium Carbide. 



tion product, could it be carried out, would be interesting 

 in this connection. 



It may be remarked that the phenomena above described 

 constitute an excellent micro-test for calcium carbide. 



Calcium cyanamide. — This substance is formed directly 

 from calcium carbide when it is heated in contact 

 with air '(nitrogen) at 900° C. and is usually present in 

 commercial carbide. Its crystalline and optical proper- 

 ties were first worked out, we believe, by Professor Moses 

 and are briefly as follows : 



System rhombohedral. Cleavage rhombohedral, per- 

 fect, angle 74°, calculated from an apparent angle as 

 measured under the microscope of 68°. There is a poor 

 cleavage or parting parallel to the base ; rarely shows a 

 twinning, probably parallel to the cleavage rhombohedron. 



Colorless, index of refraction of ordinary ray 1.60 ; of 

 extraordinary very high but undetermined. 



Double-refraction exceedingly strong, at least twice 

 that of calcite, or above 0.35. Optically positive. 



The chief point of interest is the enormous double- 

 refraction of this substance. 



Other substances, — In commercial carbide beside cyan- 

 amide, unconverted carbon, crystallized oxide of alumina 

 (corundum), and lime occur as accessories in variable 

 amounts. 



. Massachusetts Institute of Technology, 

 Cambridge, Mass., April, 1921. 



