514 Mr. T. Graham on the Absorption and 



second charge, 5*12 cub. centims. of gas were given up in an 

 hour, of which 4*4 were hydrogen; and lastly, 3'76 cub. cen- 

 tims. in an hour, of which 3*42 were hydrogen. Hence, occluded 

 by 1 vol. wrought platinum — 



5*53 vols, hydrogen. 



493 „ 



3-83 „ „ 



The volume of occluded hydrogen is much larger than in the 

 fused platinum, or even in the spongy platinum. It exhibits a 

 tendency to fall off on repeating the experiment. The declension 

 in absorbing-power may possibly be connected with the reduced 

 duration of the exposure to hydrogen of the metal while cooling. 



7. Wrought platinum, which had been formed many years 

 ago into a small tube, weighing 64*8 grms., 0*322 metre in 

 length and 5 millims. in diameter, was cut into three equal 

 lengths for convenience in placing the metal within the porcelain 

 tube, to be heated and charged with dry hydrogen. By an 

 hour's exhaustion afterwards the platinum yielded 9 '2 cub. cen- 

 tims. gas, of which 8*9 were hydrogen. The volume of the pla- 

 tinum itself was 3'9 cub. centims. ; and one volume of metal had 

 therefore occluded 2*28 vols, hydrogen, measured at about 20° C. 

 In all such experiments, besides blowing out the free hydrogen 

 by air, the apparatus was also thoroughly exhausted by the 

 Sprengel pump in the cold, before the occluded hydrogen was 

 extracted. 



The lustre and appearance of the metallic platinum was not 

 altered by the ingress of the hydrogen ; but after the escape of 

 the gas the platinum appeared whiter in colour, and the surface 

 was covered by minute blisters. 



Repeating the experiment, the gas collected by an hour's ex- 

 haustion was 8-7 cub. centims., of which 8*46 cub. centims. were 

 hydrogen. Here the metal occluded 2*8 vols, of hydrogen. 



The same platinum was a third time charged with hydrogen ; 

 but on this occasion the platinum was placed in a tube of hard 

 glass, and the tube connected with the air-exhauster. The glass 

 tube was heated by an oil-bath, and the platinum kept in vacuo 

 at a temperature of 220° C. for an hour. Not a bubble of gas 

 was evolved. The glass tube was afterwards heated by a small 

 Bunsen buruer, which was calculated to give a degree of heat 

 little short of visible redness; still no hydrogen came off. The 

 tube was now heated sufficiently to soften glass (500°) . Gas 

 began to come off, of which 1*8 cub. centim., containing 1:72 

 hydrogen, were collected in ten minutes. The glass tube having 

 cracked, the whole apparatus was allowed to cool, and the plati- 

 num transferred to a porcelain tube. Further heated by a com- 



