1880.] Compounds of Carbon with Hydrogen and Nitrogen. 155 



current capable of producing an arc between carbon poles in air 

 of about 10 millims. in length. The carbon poles used were 

 3 millims. in diameter, and had been previously purified by prolonged 

 heating: in a current of chlorine. This treatment, though it removes 



a large part of the metallic impurities present in the commercial 

 carbons, will not remove the whole, so that lines of calcium, iron, 

 magnesium, and sodium may still be recognised in the arc. Besides 

 the traces of metallic impurities a notable quantity of hydrogen 

 al ways remains unremovable by treatment with chlorine ; and we are 



