and Allied Problems. 169 



boiling point is about one-fifth that of liquid air under similar 

 conditions. It does not exceed one thirty-fifth part the surface 

 tension of water at the ordinary temperature. 



The refractive index of liquid hydrogen, determined by 

 measuring the relative difference of focus for a parallel beam 

 of light sent through a spherical vacuum vessel filled in succes- 

 sion with water, liquid oxygen, and liquid hydrogen, gave the 

 value 1*12. The theoretical value of the liquid refractive 

 index is I'll at the boiling point of the liquid. This result is 

 sufficient to show that hydrogen, like liquid oxygen and nitro- 

 gen, has a refractivity in accordance with theory. 



Free hydrogen, helium, and neon have been separated from 

 air by two methods. The one depends on the use of liquid 

 hydrogen to boil the dissolved gases out of air kept at a tem- 

 perature near the melting point of nitrogen ; the other on a 

 simple arrangement for keeping the more volatile gases from 

 getting into solution after separation by partial exhaustion. By 

 the latter mode of working something like l/34:000th of the 

 volume of the air liquefied appears as uncondensed gas. The 

 latter method is only a qualitative one for the recognition and 

 separation of a part of the hydrogen in air. In a former 

 paper on the " Liquefaction of Air and the Detection of Impur- 

 ities,"* it was shown that 100 cc. of liquid air could dissolve 

 20 cc. of hydrogen at the same temperature. The crude gas 

 separated from air by the second method gave on analysis — 

 hydrogen 32'5 per cent., nitrogen 8 per cent., helium, neon, 

 &c, 60 per cent. After removing the hydrogen and nitrogen 

 the neon can be solidified by cooling in liquid hydrogen and 

 the more volatile portions separated. 



There exists in air a gaseous material that may be separated 

 without the liquefaction of the air. For this purpose air has 

 to be sucked through a spiral tube filled with glass wool im- 

 mersed in liquid air. After a considerable quantity of air has 

 been passed, the spiral is exhausted at the low temperature of 

 the liquid air bath. The spiral tube is now removed and 

 allowed to heat up to the ordinary temperature, and the con- 

 densed gas taken out by the pump. After purification by 

 spectroscopic fractionation the gas filled into vacuum tubes 

 gives the chief lines of xenon. The spectroscopic examination 

 of the material will be dealt with in a separate paper by 

 Professor Liveing and myself. A similar experiment made 

 with liquid air kept under exhaustion, the air current allowed 

 to circulate being under a pressure less than the saturation 

 pressure of the liquid to prevent liquefaction, resulted in cryp- 

 ton being deposited along with the xenon. 



A study of fifteen electric-resistance thermometers as far as 

 the boiling point of hydrogen, has been made, and the results 

 * Chem. Soc. Proc, 1897. 



