1869.] 



of Hydrogen to Palladium. 



219 



It appears to follow that hydrogenium is magnetic, a property which 

 is confined to metals and their compounds. This magnetism is not per- 

 ceptible in hydrogen gas, which was placed both by Faraday and by 

 M. E. Becquerel at the bottom of the list of diamagnetic substances. This 

 gas is allowed to be upon the turning-point between the paramagnetic and 

 diamagnetic classes. But magnetism is so liable to extinction under the 

 influence of heat, that the magnetism of a metal may very possibly disappear 

 entirely when it is fused or vaporized, as appears to be the case with 

 hydrogen in the form of gas. As palladium stands high in the series of 

 the paramagnetic metals, hydrogenium must be allowed to rise out of 

 that class, and to take place in the strictly magnetic group, with iron, 

 nickel, cobalt, chromium, and manganese. 



5. Palladium with Hydrogen at a high Temperature. — The ready per- 

 meability of heated palladium by hydrogen gas would imply the reten- 

 tion of the latter element by the metal even at a bright red heat. The 

 hydrogenium must in fact travel through the palladium by cementa- 

 tion, a molecular process which requires time. The first attempts to 

 arrest hydrogen in its passage through the red-hot metal were made by 

 transmitting hydrogen gas through a metal tube of palladium with a vacuum 

 outside, rapidly followed by a stream of carbonic acid, in which the metal 

 was allowed to cool. When the metal was afterwards examined in the usual 

 way, no hydrogen could be found in it. The short period of exposure to 

 the carbonic acid seems to have been sufficient to dissipate the gas. But 

 on heating palladium foil red-hot in a flame of hydrogen gas, and suddenly 

 cooling the metal in water, a small portion of hydrogen was found locked up 

 in the metal. A volume of metal amounting to 0*062 cubic centim., gave 

 0*080 cubic centim. of hydrogen ; or, the gas, measured cold, was 1*306 times 

 the bulk of the metal. This measure of gas would amount to three or four 

 times the volume of the metal at a red heat. Platinum treated in the 

 same way appeared also to yield hydrogen, although the quantity was too 

 small to be much relied upon, amounting only to 06 volume of the metal. 

 The permeation of these metals by hydrogen appears therefore to depend on 

 absorption, and not to require the assumption of anything like porosity in 

 their structure. 



The highest velocity of permeation observed was in the experiment where 

 four litres of hydrogen (3992 cub. centims.) per minute passed through a 

 plate of palladium 1 millim. in thickness, and calculated for a square metre 

 in surface, at a bright red heat a little short of the melting-point of gold. 

 This is a travelling movement of hydrogen through the substance of the 

 metal with the velocity of 4 millimetres per minute. 



6. Chemical Properties. — The chemical properties of hydrogenium also 

 distinguish it from ordinary hydrogen. The palladium alloy precipitates 

 mercury and calomel from a solution of the chloride of mercury without 

 any disengagement of hydrogen ; that is, hydrogenium decomposes chloride 

 of mercury, while hydrogen does not. This explains why M. Stanislas 



r2 



