300 HYDROGEN AS A GAS AND AS A METAL. 



creased, since reduction in length is accoinj^auied by a proportional 

 increase in other dimensions. 



It is found that this palladium foil charged with hydrogen possesses 

 most powerful reducing properties ; that the hydrogen within it is just 

 as capable of reducing silver salts as a metallic layer of zinc would be. 

 As illustrating this point, we may cite an experiment : A plate of pal- 

 ladium foil was cliarged with hydrogen, as above described, and then 

 immersed in a solution of corrosive sublimate ; almost immediately a 

 white precipitate of calomel made its appearance, and, when the action 

 I)roceeded a little further, mercury was reduced. On repeating this 

 experiment with a slightly alkaline solution of nitrate of silver, the 

 metal was quickly thrown down on the palladium plate, and, when an 

 alkaline solution of gold was used, the metal was likewise precipitited. 

 These j)recipitates were obtained under circumstances in which the ordi- 

 nary hydrogen gas or palladium foil alone would have been quite inca- 

 pable of effecting reduction. 



We have already seen that hydrogen can be liberated from tlie charged 

 palladium by presenting to it oxygen m conditione na.scenti, but it can 

 also be set free by heat, or by reduction of the pressure of the atmo- 

 sphere surrounding the charged plate. If a palladium wire be made to 

 absorb as much hydrogen as it can take up, and if the tip of the wire 

 be heated in the flame of a spirit-lamp, hydrogen gas is liberated, and 

 burns on the surface of the palladium, the flame continuing until all the 

 gas has been set free. Again, if a similarly charged wire be placed 

 under the receiver of an air-pump and tbe air exhausted, the hydrogen 

 is completely liberated in its ordinary gaseous condition. 



In order to complete this account of hydrogenium, it is only neces- 

 sary to mention that its density is stated to be nearly 2, or about equal 

 to the specific gravity of the metal magnesium ; but the means by which 

 Professor Graham has arrived at this result, though very ingenious, are 

 so unsatisfactory that we must take this estimate as being a mere ap- 

 proximation to the truth. In all probability we must wait for the accu- 

 rate determination of the specific gravity of hydrogenium until the metal 

 itself will have been isohited in a pure condition. 



Thus, in the course of this lecture, we have liberated hydrogen, " as 

 a ^a.s'," from water, and in this condition have studied some of its proper- 

 ties. Again, we have made this remarkable element alloy itself with 

 palladium ; and when thus appearing in the guise of " a metal," we have 

 noted the chief phenomena it gives rise to. And now, like the bird 

 from its cage, we will set free this hydrogen from its prison-house of 

 palladium, and let it mingle with the mighty aerial ocean in which we 

 live and move. 



