The solubility of hydrogen in platinum has been studied by Sieverts, who has shown that the gas is less soluble in compact platinum than in the same weight of iron or nickel. At constant pressure the solubility rises with the temperature, whilst at constant temperature the amount of hydrogen absorbed is directly proportional to the square root of the pressure. On cooling, all the hydrogen absorbed at higher temperatures by the metal is evolved.
Platinum does not absorb carbon dioxide or sulphur dioxide. Platinum which has been heated to a high temperature in a current of hydrogen is usually found to have undergone a slight permanent change, its melting-point being depressed and its ductility reduced. This, however, appears to be due to the absorption of small quantities of carbon from traces of organic impurity in the hydrogen, and not to the influence of the pure hydrogen itself. |