182 BELL SYSTEM TECHNICAL JOURNAL 



in palladium, cerium, thallium, zirconium, titanium, tantulum, and 

 vanadium. The solubility changes of hydrogen in palladium are 

 particularly interesting. One volume of this metal absorbs 670 to 

 800 volumes of hydrogen at 20° C, 50.6 volumes at 138° C, and in 

 the liquid state at 1600° C. only 4.3 volumes.'^ 



Since the solubility of gases in aqueous liquids decreases with 

 increasing temperature, and since these data form the bulk of the total 

 available, some workers have suggested that the increase in solubility 

 of gases in metals with increasing temperature is anomalous. No 

 anomaly appears, however, when the solubility relationship is con- 

 sidered in the light of van't Hoff's law of mobile equilibrium. This 

 law states that when the temperature of a system in equilibrium is 

 raised only that reaction can occur which is accompanied by an 

 absorption of heat, that is, an endothermal reaction. The increasing 

 solubility of gases in metals with increasing temperature, therefore, 

 should be taken as evidence of an endothermic reaction rather than 

 as an anomaly. 



Data are available which show that increasing solubility of gases 

 with increasing temperature is not limited to gas-metal systems. 

 Just 1* has shown that the solubility of hydrogen, carbon monoxide, 

 and nitrogen in carbon disulphide, nitrobenzene, acetone, and other 

 organic solvents increases with increasing temperature. Lannung ^^ 

 has reported data showing that the solubility of argon, neon, and 

 helium in methyl alcohol, and acetone increases with increasing 

 temperature. In this respect the gas-metal systems seem to be 

 similar to some of the gas-organic liquid systems. 



Another fairly well known influence of temperature on the quantity 

 of gas absorbed by a metal is due to an allotropic change in the 

 structure. That the amount of gas absorbed by a metal changes 

 abruptly when the allotropic form changes, is illustrated by the iron- 

 nitrogen system. One hundred grams of iron heated to 878° C. 

 absorbs only 1.6 milligrams of nitrogen, but at 930° C, in the gamma 

 modification, it takes up 21.6 milligrams. '^ 



The Effect of Pressure on the Solubility of Gases in Metals 



The effect of changes in pressure on the solubility of gases in metals 

 has been studied intensively by Sieverts. He made the discovery 

 that the quantity of gas dissolved in a metal at constant temperature 



^^ Loc. cit. 



'^ Just, Zeit. Phys. Chem., 37, 342 (1901). 



'^Lannung, Jour. Am. Chem., Soc, 52, 73 (1930). 



