218 Dr. W. A. Tilden. On the Condition in which [Jan. 23, 



January 23, 1896. 



Sir JOSEPH LISTER, Bart, President, in the Chair. 



A List of the Presents received was laid on the table, and thanks 

 ordered for them. 



The following Papers were read : — 



I. " An Attempt to Determine the Condition in which Helium 

 and the Associated Gases exist in Minerals." By W. A. 

 Tilden, D.Sc, F.R.S. Received January, 13, 1896. 



Argon and probably also helium having, it is supposed, monatomic 

 molecules, the chemical inactivity which they have been found to 

 exhibit cannot be accounted for by the hypothesis usually applied to 

 the case of nitrogen. Hence it appears probable that they will not 

 be found, like nitrogen, to enter into combination with other elements 

 at such high temperatures as are ordinarily attainable, and experience, 

 so far, has shown this to be the case. It also appears improbable that 

 in the minerals from which the mixture of gases containing helium 

 has been extracted this element exists in a state of ordinary chemical 

 combination, for on treating the mineral with acids no compound of 

 helium with hydrogen has yet been observed, and the components of 

 the minerals are of a kind which is commonly regarded as chemically 

 saturated. 



I thought it would be interesting to find out if possible whether 

 the gas evolved on treatment with acids or on the application of heat 

 was enclosed in cavities or was in the state of so-called " occlusion." 

 Supposing no evidence to be forthcoming that the gas was locked up 

 in one of these two ways, then some new form of chemical combina- 

 tion would have to be looked for. 



Some monazite, for which I was indebted to the kindness of Pro- 

 fessor Lockyer, was first examined. The powdered mineral was 

 enclosed in a hard glass bulb, which was sealed on to the Sprengel 

 pump and exhausted. The balb was then heated in successive 

 stages to the temperature of boiling sulphur, 446°. The first evolu- 

 tion of gas occurred at 60°, but this consisted of carbon dioxide 

 with water vapour, and the temperature being kept constant a vacuum 

 was soon re-established. From 70° to 80° a little more of the same 

 gas was evolved, und on raising the temperature successively to 100°, 

 115°, 130°, small quantities, nearly equal, of carbon dioxide were 



