Dialytic Separation of Gases by Colloid Septa. 513 



comparison with the earlier observations on the penetration of a 

 platinum septum by hydrogen gas, that both wire and tube had 

 been drawn out from the same mass of fused metal. No iridium 

 had been added to this platinum, as is sometimes done to increase 

 the elasticity of the metal. The absorption of hydrogen is small, 

 amounting, according to the mean of the four observations, to 

 17 per cent, of the volume of the platinum. At the temperature 

 of a low red heat, when the absorption took place, the gas would 

 be considerably dilated, to the extent of at least three times its 

 volume stated above, or to about 51 per cent, (half the volume) 

 of the platinum. It is to be considered whether an absorption 

 of half a volume of gas would be sufficient to account for the 

 observed penetration of a septum of metal 1*1 millim. in thick- 

 ness. The data appear to favour an affirmative conclusion ; but 

 their value cannot be very decidedly estimated. 



It appears necessary to recognize in platinum a new property, 

 a power to absorb hydrogen at a red heat, and to retain that gas 

 at a temperature under redness for an indefinite time. It may 

 be allowable to speak of this as a power to occlude (to shut up) 

 hydrogen, and the result as the occlusion of hydrogen by platinum. 



The observation was extended to platinum in other conditions 

 of form, but where, it is to be observed, the metal had not been 

 fused, but only welded, and was not of recent manufacture. 



5. Of the grey pulverulent spongy platinum, prepared from the 

 ammonio-chloride, 22*2 grms. were heated by the combustion- 

 furnace, and for half an hour allowed to cool gradually in dry 

 hydrogen gas, as in the preceding experiments. The volume of 

 the platinum is 1*032 cub. centim. by calculation. In the first 

 experiment it yielded to heat and the action of the Sprengel 

 pump 2*2 cub. centims. of a gas which burned like hydrogen. 

 In a second experiment the platinum yielded in one hour (when 

 it appeared to be exhausted) 1*7 cub. centim. of gas, found by 

 explosion to consist of hydrogen 1*52 cub. centim., and nitrogen 

 0'18 cub. centim. Here one volume of spongy platinum appears 

 capable of occluding 



1'48 vol. hydrogen. 



6. Wrought platinum, in the form of plate from an old cru- 

 cible cut up, after washing and ignition, was charged with hy- 

 drogen three times in succession. The weight of the platinum 

 was 24"1 grms., and its volume 1*12 cub. centim. It yielded in 

 seventy-five minutes 4*19 cub. centims. of gas, and in thirty 

 minutes further 1*5 cub. centim. more, making together 5*69 

 cub. centims., of which 4*94 cub. centims. proved to be hydrogen ; 

 therm. 14 0, 2, barom. 760 millims. Not a trace of carbonic acid 

 was found in the gas before or after explosion. Again, after a 



Phil. Mag. S. 4. No. 219. Suppl. Vol. 32. 2 L 



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