The Occlusion of Gases. 457 



centimetres of gas, of which 1'93 proved to be pure 

 hydrogen. 



The weight of the metal being divided by its specific 

 gravity (201 -f 2 1*5) gives the volume of the metal— 9 '34 cubic 

 centimetres ; hence the one volume of platinum held (the gas 

 being measured cold), 0'207 volumes of hydrogen. It must 

 be admitted, therefore, that platinum has a power to absorb 

 hydrogen at a red heat, and . to retain it for an indefinite 

 period, to this power Mr. Graham has given the name of 

 occlusion (a shutting up) of hydrogen by the metal. 



Hammered platinum has a much higher absorbing or 

 " occluding" power than the fused metal, probably owing to a 

 mechanical difference in the texture, a specimen, in the form of 

 tube, occluded 2'8 times its volume of hydrogen; the same 

 platinum again charged with hydrogen was sealed up in a 

 glass tube, after two months it gave on distillation in vacuo 

 2*28 times its volume of gas, tending to prove that the 

 hydrogen had been retained by the platinum without loss. 



It has already been stated that the transmission of hydrogen 

 through palladium was far more striking than in the case of 

 platinum, the permeation taking place at a far lower tem- 

 perature. The results given by the occlusion of hydrogen by this 

 metal were also most remarkable. A specimen of foil rolled 

 from wrought palladium, weighing 1'58 grammes, was exposed 

 to hydrogen, at a temperature between 90° and 78° C. for three 

 hours, and then allowed to cool slowly in a stream of the gas. 

 The metal was then transferred to a glass tube, which was 

 exhausted in the usual way, and on being heated with a gas 

 flame the palladium gave off gas in a continuous stream for 

 twelve minutes, when the evolution ceased. The volume of gas 

 amounted to 85*56 cubic centimetres. The palladium having 

 occluded 643'3 times its volume of hydrogen. As in the case 

 of the platinum the melted metal does not possess the power 

 to the same degree as the wrought metal. The specimen 

 examined absorbed about 347 times its volume of hydrogen. 



Each metal exerts a selective power for gases. Copper 

 wire occludes 0.306 times its volume of hydrogen. Gold 

 cornets* from the refuse of assays were examined without 

 preliminary treatment, 93 grammes, having a volume of 

 4.83 cubic centimetres, gave, on heating in vacuo;, 10.25 cubic 

 centimetres of gas, which consisted principally of carbonic oxide. 

 The same cornets, though they never assumed so much gas as 

 they acquired in the muffle, still occluded 0.33 times their 

 volume of carbonic oxide, and 0.48 times their volume of 

 hydrogen. 



* When the button of gold is removed from the assay furnace it is rolled into 

 a riband and twisted into a flat spiral, to which the name of " cornet" is given. 



