1899.] 



on Liquid Hydrogen. 



11 



from the point at which the metal would theoretically hecome a 

 perfect conductor. The effect of cooling platinum from the boiling 

 point of liquid oxygen to that of liquid hydrogen is to diminish its 

 resistance to one-eleventh. 



The difficulties in liquefying hydrogen caused by the presence of 

 air in the gas have been referred to,* and later experiments had for 

 their object the removal of this fruitful source of trouble. This is 

 by no means an easy task, as quantities amounting to only a fraction 

 of one percent, accumulate in the solid state, and eventually choke the 

 nozzle of the apparatus, necessitating the abandonment of the opera- 



Temperature in degrees Centigrade. 

 Fig. 3. 



tion. Later experiments enabled me to procure a larger supply of 

 liquid hydrogen with which the determination of certain physical con- 

 stants has been continued. The first observations made with a pure 

 platinum-resistance thermometer had given — 238° as the boiling 

 point. A new thermometer, constructed of platinum from a different 

 source, gave practically the same value. As these results might be 

 affected by some constant error, the determination was checked by 

 employing a thermometer constructed from an alloy of rhodium and 



* ' Prnoeedinss,' 1898, 14, 130. 



