410 Professor Sir James Deivar [June 5, 



be about 5' (to which several observations of mj own point) we 

 must start from 15° to have the same temperature fall of 3 to 1. 

 But that would require a large and elaborate plant, and with the 

 mass of gases in circulation and the time required, the fight against 

 any influx of heat from the outside becomes harder. 



There is no intermediate fixed point between 65° and 20°, so that 

 a descent of 15' has to be effected by regenerative methods in the 

 liquefaction of hydrogen, and a similar rate of descent would have to 

 be achieved before helium could be liquefied. In order to keep the 

 circulation of helium up for four minutes in my apparatus, about 

 6 litres of hydrogen disappeared, and during all the time of the 

 operation the impurities in the gas were accumulating at the valves. 



There are other difficulties to be overcome before the apparatus 

 could be worked with success. Hydrogen is cheap enough, helium 

 very costly. For years our supply has come from the King's Well at 

 Bath, which gives off a gas (largely nitrogen) containing ^^Vo of its 

 volume of impure helium. We have to deal with very large volumes 

 of gas, and after years of work I lost all my treasured store of helium. 

 We know now that helium is more common than we had at first 

 thought. Our atmosphere contains o'soVoo of lielium, and in 

 several springs it is more abundant than at Bath. The gases given 

 off by certain springs in France contain more than 2 per cent, of 

 helium. A similar amount has also been found in the natural gas 

 of a. Xorth American town. With 100 or 200 litres of helium at 

 the experimenter's disposal, it would be easy to prove the success 

 or failure of the regenerative method.* 



For the present I have made further experiments on helium 

 absorption by charcoal. With helium, the absorption only begins at 

 the lowest realisable temperatures, but when we come to the boiling- 

 point of hydrogen the charcoal absorbs 200 times its volume of 

 helium, and the curve shows that helium at its own boiling-point 

 of about 5' would most probably be absorbed to the same extent 

 as hydrogen at its boiling-point. The absorption of gases by charcoal 

 was accompanied by evolution of heat shown in the following table : 



Heat Evolution Determined by Change of Gas Tensions at Different 

 Temperatures (Concentration Constant) in each Experiment. 



* Helium was liquefied by Professor Dr. Kamerlingh Onnes, of Leiden 

 University, on July 9, 1908. 



