86 Prof. J. Dewar. Studies on the Electric Arc. [Jan. lf> T 



vessel allowed the glass tube coming from the positive pole to pass 

 with little friction, through which the products from the arc were 

 drawn. This annular vessel was very convenient, not only for exa- 

 mining the products formed in the arc, but also those formed outside 

 of it, and the water flowing round it served the double purpose of 

 keeping it cool and enabling a determination of the amount of total 

 radiation in heat units to be made. 



Fig. 1. 



Vessels containing sulphuric acid and phosphoric anhydride were 

 placed inside the cylinder in order to dry the interior as completely as 

 possible. 



Numerous experiments made by forcing perfectly dry air into the 

 vessel through the tube A, and drawing it out by the tube B through 

 a weighed sulphuric acid bulb, gave after an hour a few milligrams of 

 water, owing no doubt to some slight defect in the soldering of the tin, 

 which allowed a capillary film of water to diffuse into the interior 

 space. 



When the ordinary Siemens' carbons were burnt in this almost 

 dry atmosphere, the yield of hydrocyanic acid was still very marked, 

 purified carbons yielding the same results. 



