388 



HON. R. J. STRUTT ON THE LEAST POTENTIAL DIFFERENCE 



have destroyed the equality of these pressures. The nitrogen employed was 

 prepared by the action of heat on ammonium nitrite. Ammonium chloride solution 

 was contained in a flask, fitted with an india-rubber cork, through which passed 

 a dropping funnel and an exit tube for the gas. Potassium nitrite solution was 

 contained in the funnel, and could be dropped into the warmed ammonium chloride. 

 The gas passed through strong sulphuric acid and caustic potash solutions, each 

 contained in ordinary potash bulbs. From these it passed into a chamber containing 

 phosphoric anhydride, closed at either end by taps. An approximate vacuum was first 

 made in the entire arrangement by means of a water pump. This reduced the pressure 

 to something less than a centimetre of mercury. Gas was then liberated so as to 

 slowly fill the apparatus up to atmospheric pressure. A current was allowed to 

 flow for some time through the phosphoric anhydride chamber, so as to wash out all 

 traces of air. When this had been done the chamber was shut off, and the gas left in 

 it all night, so that it might become thoroughly dry. It could then be admitted 

 through a tap into the sparking vessel. 



Diagram No. 3. Nitrogen. 



700 



8 



8 



4 



Cu. ve N 



8 



8 



n 



to 



40 60 



mm. of Mercury. 



6O 



70 



so 



After the gas had been passed several times through the alloy, the following 

 measurements were taken (Diagram No. 3, curve 1) : 



