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384 HON. E. J. STRUTT ON THE LEAST POTENTIAL DIFFERENCE 



Diagram No. 1. Air. 



Pressure, mm. of Mercury. 



Hydrogen. 



We now come to the experiments on hydrogen. The hydrogen was prepared first 

 by the electrolysis of caustic potash solution, and dried by means of phosphoric 

 anhydride. The sample of gas thus prepared gave a minimum spark potential of 

 300 volts. The readings were as follows : 



These results are plotted on Diagram No. 2. 



It will be seen that the minimum is very nearly 300 volts. 



