56 Lord Rayleigh. On the Amount of Argon and 



27. A mixture of soda-lime and sulphur consisting of polysulph- 

 ides causes no change of volume in a current of helium passed over 

 it at a bright red heat. 



28. Induction sparks in an ozone apparatus passed through a mix- 

 ture of helium with benzene vapour in presence of liquid benzene 

 for many hours, gave no change of volume. The benzene was, of 

 course, altered, but the sum of the pressures of the helium and the 

 benzene- vapour remained as at first. Had helium been removed, 

 contraction would have occurred. 



This ends the catalogue of negative experiments. Any compound 

 of helium capable of existence will probably be endo thermic, and the 

 two methods of producing endothermic compounds, where no simul- 

 taneous exothermic reaction is possible, are exposure to a high tem- 

 perature, at which endothermic compounds show greater stability, 

 and the influence of the silent electric discharge. These methods 

 have been tried, so far in vain. There is, therefore, every reason to 

 believe that the elements, helium and argon, are non-valent, that is, 

 are incapable of forming compounds. 



"On the Amount of Argon and Helium contained in the 

 Gas from the Bath Springs."* By LORD RAYLEIGH, 

 Sec. R.S. Received April 30, Read May 21, 1896. 



The presence of helium in the residue after removal of nitrogen 

 from this gas was proved in a former paper, f but there was some 

 doubt as to the relative proportions of argon and helium. A fresh 

 sample, kindly collected by Dr. Richardson, has therefore been ex- 

 amined. Of this 2500 c.c., submitted to electric sparks in presence 

 of oxygen, gave a final residue of 37 c.c., after removal of all gases 

 known until recently. The spectrum of the residue, observed at 

 atmospheric pressure, showed argon, and the D 3 line of helium very 

 plainly. 



The easy visibility of D 3 suggested the presence of helium in some 

 such proportion as 10 per cent., and this conjecture has been con- 

 firmed by a determination of the refractivity of the mixture. It may 

 be remembered that while the refractivity of argon approaches 

 closely that of air, the relative number being 0'961, the refractivity 

 of helium (as supplied to me by Professor Ramsay) is very low, 

 being only 0*146 on the same scale. If \ve assume that any sample 



* I am reminded by Mr. Whitaker tliat helium is appropriately associated with 

 the Bath waters, which, according to some antiquaries, were called by the Eomans 

 Aqua Soils. 



t 'Boy. Soc. Proc.,' vol. 59, p. 206, 1896. 



