780 Dr. R. v. Hirscli and Mr. F. Soddy : A Gas 



time? less in nitrogen than in hydrogen. In the case of 

 carbon monoxide and oxygen, the values o£ p 2 Y are about 

 two-thirds that of hydrogen divided by the numbers 16 and 

 14 respectively. 



The behaviour of the gas evolved from the electrodes 

 indicates that it is not a mixture but a pure gas and that its 

 molecular weight is 4 or some multiple. 



In the present paper the nature of this gas is further 

 examined. The first point Mas to see if the gas was 

 helium. 



The spectrum was the familiar one always obtained when 

 a new spectrum tube is exhausted and the electrodes heated 

 with a discharge, and consisted of hydrogen and the 

 secondary spectrum of hydrogen together with faint indica- 

 tions of the strongest bands of carbon dioxide. The gas 

 was subjected to the action of calcium volatilized by an 

 electric furnace in the manner recently described by one of us 

 (Soddy, Proc. Hoy. Soc. vol. Ixxviii. A. p. 429, 1907), and 

 was found to be completely absorbed leaving no trace of 

 helium. 



The quantities of the unknown gas obtainable are too small 

 for ordinary analysis, so it was attempted to identify it by 

 its electrical behaviour, taking the values of p 2 V for a variety 

 of different substances in the hope of finding one giving a 

 value one-fourth that of hydrogen. 



The experimental arrangement was similar to that used 

 before. The current was obtained from an 8-plate Wimshurst 

 machine producing nearly half a milliampere when at full 

 speed, so that the independence of discharge potential on 

 the current could be verified within a larger range than 

 formerly, in fact up to the point where the tube became per- 

 ceptibly heated. The potentials were measured directly by a 

 Kelvin electrostatic voltmeter. 



In the search for the unknown gas the most valuable hint 

 given by earlier results is the fact, that for mixtures p 2 Y is 

 not constant, so that pure gases only have to be tried. But 

 it was found advisable again to ascertain this point by trying 

 several mixtures, between the components of which chemical 

 action was excluded, special care being taken that the mixtures 

 did not change during the investigation. The results are 

 given in the following; tables : — 



