and Ohmic Resistance of Gases. 



355 



desired pressure. The bulbs of the pump, aggregating over 

 a litre in volume, were always in communication with the 

 PI acker tube while the circuit was closed, so that the discharge 



took place under essentially constant pressure. The hydrogen 

 was made electrolytically and purified by passing through 

 a solution of potash and over fused potash and phosphoric 

 anhydride ; the nitrogen was made by passing ammonia 

 over an excess of heated cupric oxide, through much water, 



