DIALTTIC SEPARATION OF GASES Br COLLOID SEPTA. 427 



continuous stream for twelve minutes, when it ceased. The gas amounted to 85-56 cub. 

 centims., of which 96-8 per cent, was hydrogen; therm. 17°-5, barom. 764 millims. 

 1 vol. palladium held 643-3 vols, hydrogen. 



By the care of my zealous assistant, Mr. W. C. Roberts, the hydrogen employed in 

 these experiments was purified to the highest degree by passing it in succession through 

 alcohol, water, caustic potash, and tubes of 0*7 metre each, filled with broken glass 

 impregnated with nitrate of lead, sulphate of silver, and oil of vitriol. The gas was 

 inodorous, and bui-ned with a barely visible flame. 



No alteration was sensible in the metallic appearance of the palladium-foil when 

 charged with hydrogen, or when discharged. The foU was much crumpled and rather 

 friable after repeated use ; but this may have arisen from frequent handling. 



3. Palladium appears to absorb hydrogen largely, even at natural temperatures, pro- 

 vided that the metal has been recently ignited in vacuo. The foil, without such prepa- 

 ration, was placed in a bottle of pure hydrogen for several hours, but yielded nothing 

 when afterwards ignited in the Sprengel vacuum. The foil, however, being immediately 

 returned after cooling to a stoppered bottle containing hydrogen, and left in the gas for 

 a night, absorption now took place — air rushing in, on opening the stopper, as into a 

 partial vacuum; therm. 19°. When the palladium-foil was afterwards transferred to a 

 glass tube and connected with the Sprengel pump, it was found difficult to obtain a 

 vacuum for some time, owing to hydrogen coming off at the temperature of the atmo- 

 sphere. But after a fair vacuum was produced 6-96 cub. centims. were collected, of 

 which 6-78 proved to be hydrogen. Heat was then applied, and 42 cub. centims. came 

 over in five minutes, making altogether more than 50 cub. centims., or 376 volumes of 

 gas. The absorption of hydrogen appears, then, to be suspended at a low temperature, 

 unless the condition of the metal be favourable. The action of a plate of clean platinum 

 in determining the combustion of explosive gas is equally critical at a low temperature. 



4. A different specimen of palladium-foil, weighing 5-76 grms., and having a volume 

 of 0-485 cub. centim., was charged with hydrogen, and discharged, more than once. 

 In the second experiment, the foil was heated in hydrogen at 100° for three hours. 

 Distilled afterwards in a porcelain tube at a low red heat in the usual way, the palla- 

 dium was found to have absorbed, at 100°, 



347'7 vols, of hydrogen measured at 18°-2 C. and barom. 756 millims. 



5. So large an absorption of hydrogen should increase the weight of the palladium 

 sensibly, notwithstanding the lightness of the gas. One litre, or 1000 cub. centims., of 

 hydrogen at 0° C. and 760 millims. weighs 0-0896 grm. Of new palladium-foil, 

 believed to be from fused metal, 5-9516 grms. increased to 5-9542, or by 0-0026 grm., 

 when the metal was charged with hydrogen at 100° for four hours. This amounts to 

 only 29-01 cub. centims. of hydrogen at 0° C. and 760 millims. barom. The gas actually 

 extracted aftei-wards from the palladium did not exceed 34*2 cub. centims. at 19° C, 

 and barom. 758 millims., equivalent to 31-84 cub. centims. at 0° C. and 760 millims. 



