456 Mr. Graham's Recent Discoveries. 



The comparison follows, penetration of hydrogen through 

 a square metre of the rubber in one minute, at a temperature 

 of 20° C— 127 cubic centimetres, through the palladium =42 3 

 cubic centimetres, at a temperature of 265° C. 



It has been shown that oxygen could be partially separated 

 from atmospheric air by the septum of india-rubber, while' 

 platinum and palladium only permit hydrogen to pass, 

 apparently to the exclusion of every other gas. Therefore 

 when the palladium tube was heated to 270° C. in an atmo- 

 sphere of coal gas consisting of a mixture of 45 per cent, 

 marsh gas, with 40 per cent, free hydrogen, the gas pene- 

 trating the metal and delivered by the mercurial exhauster 

 contained no trace of carbon compound, but was pure 

 hydrogen. 



It is now necessary to consider the nature of these trans- 

 missions in the case of the rubber and metal respectively. 



In the passage of gas through the india-rubber, it has 

 been shown that the colloid substance possessed the power of 

 absorbing the gas. Is the penetration of the platinum due to 

 the same cause ? 



The following experiments were devised in order to deter- 

 mine this : — 



The metal was first carefully cleaned by washing in alkali, 

 and subsequently with distilled water ; it was then introduced 

 into a porcelain tube glazed both inside and out, and provided 

 with corks well covered with fused gutta percha, each cork 

 was fitted with a fine quill tube. The one quill tube, a, being 

 connected with the mercurial exhauster, the other being then 

 closed. It is evident, therefore, that the apparatus afforded a 

 means of heating the metal in vacuo, and of transferring any 

 gas that might be distilled over. 



FIG. 2 . 



||| I I llllllll Ijlf 



Wire of fused platinum weighing 200 grammes was heated 

 to bright redness, and allowed to cool slowly in a stream of 

 pure and dry hydrogen. 



The same wire on distillation in vacuo gave 2*12 cubic 



