32 Mr Richardson, Note on the Diffusion of Hydrogen, etc. 



dissolved in platinum was found to be 9"125 x 10 3 calories. 

 These quantities are of the same order of magnitude as the heats 

 of solution of one gram molecule of hydrogen in the metals, which 

 were found by Mond, Ramsay, and Shields* to be 8'74 x 10 3 and 

 1322 x 10 3 calories for palladium and platinum respectively. 

 It will be noticed that if the dissolved hydrogen is practically all 

 dissociated the sum of these two quantities for any one metal 

 would be the heat of solution of H 2 if no dissociation took place. 



This note will not altogether fail in its purpose if it succeeds 

 in drawing attention to the fact that fresh experiments on this 

 subject are required. No doubt accurate experiments are more 

 difficult to make with palladium than with platinum, and to 

 obtain unexceptionable results two points must be carefully borne 

 in mind. One is to make certain of the pressure law by using as 

 great a range of pressure differences as possible, and the other is 

 never to let the external pressure become so great as to admit of 

 the formation of two immiscible solid hydrogen solutions inside 

 the metal. 



* Phil. Trans. A. Vol. cxci. p. 105. 



