512 Mr. T. Graham on the Absorption and 



alone for an hour to drive off any natural gaseous product ; and 

 then dry hydrogen gas was admitted to the porcelain tube, the 

 gas being evolved from pure sulphuric acid and pure zinc. The 

 hydrogen was conveyed in excess into the porcelain tube, at a 

 cherry-red heat, and the temperature was then allowed to fall in 

 a gradual manner — a procedure which was found to promote the 

 absorption of the gas. The platinum was thus retained for about 

 twenty minutes in an atmosphere of hydrogen, at a temperature 

 partly above and partly below dull redness, terminating with the 

 lower temperature. After the fire was withdrawn and the tube 

 allowed to cool, air or nitrogen was driven through it, and all 

 free hydrogen thus expelled from the apparatus. 



The closed tube was now exhausted in the cold, but no hydro- 

 gen came off. The platinum being still retained in a good va- 

 cuum, heat was agaiu very gradually applied, and the action of 

 the Sprengel pump maintained. Simultaneously with the first 

 appearance of visible ignition, gas began to be evolved. In one 

 hour, the porcelain tube being heated to redness, 2*12 cub. cen- 

 tims. of gas were collected, of which about one-third was col- 

 lected in the first ten minutes. It was found, by explosion with 

 oxygen, to consist of 



Hydrogen . . . 1*93 cub. centim. 

 Nitrogen ... 0' 19 „ 



Now, taking the specific gravity of the platinum wire at 21*5, 

 the volume of 201 grms. of metal will be 9*34 cub. centims. 

 Hence one volume of platinum held, the gas being measured cold, 



0*207 vol. hydrogen. 



The platinum did not appear sensibly altered in lustre, or in 

 any other way, by its relation to the hydrogen. 



2. The same piece of platinum wire was drawn out into four 

 times its first length, and the experiment of charging with hy- 

 drogen was repeated. The platinum gave up at a red heat, 

 maintained for one hour, 1*8 cub. centim. of gas, of which 1*6 

 cub. centim. was hydrogen. Here one volume of platinum ap- 

 pears to have held 



0-171 vol. hydrogen. 



The absorption of hydrogen has not been increased by increa- 

 sing the surface of the metal. 



In two further experiments upon the same platinum wire, the 

 volume of hydrogen retained by one volume of platinum was — 



3. 0*173 cub. centim. hydrogen. 



4. 0128 „ „ 



There is an evident tendency of the hydrogen taken up to di- 

 minish in quantity. These experiments have the advantage, for 



