1907.] 



on Hifjh Vacua and Helium. 



74^ 



considerable amount of solid on the external coil, and finally the 

 internal tubes plugged. During the evaporation of the solid depos ited 

 on the coil in the fourth circulation, the composition of the gase& 

 given off in three successive portions were as follows : — 



The gas analysis suggests that the solid was composed of a mix- 

 ture of solid hydrogen and nitrogen along with dissolved helium 

 and neon. 



The gaseous portion remaining after the last circulation, on being 

 freed from hydrogen, consisted of 04 per cent, of helium and 6 per 

 cent, of neon. To this helium and neon 75 per cent, of hydrogen 

 was added, which, on passing round the regenerative circuit, yielded 

 liquid hydrogen containing 1;^ per cent, of helium in solution, along 

 with some solid presumably neon in the bottom of the vacuum vessel. 

 The final helium left uncondensed in the circuit after the removal of 

 the hydrogen contained 4 per cent, of neon. 



Now how could the hydrogen be frozen during the circulation 

 of the helium and hydrogen mixture ? An experiment made on a 

 former Friday evening with nitrogen will explain. On that occasion 

 hydrogen was allowed to bubble up through a quantity of liquid 

 nitrogen. The bubbles, in accordance with Dalton's law, being free of 

 nitrogen induce a rapid evaporation of the liquid nitrogen into them 

 as they pass through it, thus causing cooling, until the liquid nitrogen 

 becomes first viscous and finally freezes into a jelly containing spiral 

 tubes through which the hydrogen escapes. In the same way the 

 passage of the uncondensed helium through or over liquefied hydrogen 

 formed by spray on the regenerator coils lowers its temperature and 

 finally causes it to freeze. 



Such regenerative operations were carried on under considerable 

 difficulties as it was impossible to see properly what was taking place in 

 the apparatus, and at any moment the vacuum vessels might collapse. 

 On one occasion, the whole of the helium that had been accumulated 

 during 2 years was lost owing to the collapse of the glass vacuum 

 vessel containing the regenerator coil, and the experiment of accu- 

 mulating helium had to begin de novo. 



The use of charcoal provides us with a ready means of studying 

 the properties of gas mixtures containing helium. A sparking-tube, 

 having a branch charcoal bulb attached, was charged with Bath-gas. 



