THE COMPOSITION OF WATER, HYDROGEN 145 



In this condensed form it is capable of reacting on substances on which 

 it does not act in a gaseous state. There is a very intimate and evident 

 relation between the phenomena which take place in the action of 

 spongy platinum and the phenomena of the action in a nascent state. 

 The combination of hydrogen with aldehyde may be taken as an ex- 

 ample. Aldehyde is a volatile liquid with an aromatic smell, boiling at 

 21, soluble in water, and absorbing oxygen from the atmosphere, and 

 in this absorption forming acetic acid the substance which is found in 

 ordinary vinegar. If sodium amalgam be thrown into an aqueous 

 solution of aldehyde, the greater part of the hydrogen evolved combines 

 with the aldehyde, forming alcohol a substance which is also soluble 

 in water, which forms the principle of all spirituous liquors, boils at 78, 

 and which contains the same amount of oxygen and carbon as aldehyde, 

 but more hydrogen. The composition of aldehyde is C 2 H,0, and of 

 alcohol C 2 H 6 O. Reactions of substitution or displacement of metals 

 by hydrogen at the moment of its evolution are particularly nume- 

 rous. 4 "' 



Metals, as we shall afterwards see, are in many cases able to replace 

 each other ; they also, and in some cases still more easily, replace and 

 are replaced by hydrogen. We have already seen examples of this in 

 the formation of hydrogen from water, sulphuric acid, ttc. In all these 

 cases the metals sodium, iron, or zinc displace the hydrogen which occurs 

 in these compounds. Hydrogen may be displaced from many of its 

 compounds by metals by exactly the same method as it is displaced 



45 When, for instance, an acid and zinc are added to a salt of silver, the silver is 

 reduced ; but this may be explained as a reaction of the zinc, and not of the hydrogen at 

 the moment of its evolution. There are, however, examples to which this explanation 

 is entirely inapplicable ; thus, for instance, hydrogen, at the moment of its evolution, 

 easily takes up oxygen from its compounds with nitrogen if they be in solution, and 

 converts the nitrogen into its combination with hydrogen. Here the nitrogen and hydrogen, 

 so to speak, meet at the moment of their evolution, and in this state combine together. 



It is evident from this that the elastic gaseous state of hydrogen fixes the limit of its 

 energy : hinders it from entering into those combinations of which it is capable. In the 

 nascent state we have hydrogen which is not in a gaseous state, and its action is then 

 much more energetic. This is rendered very clear from the conception of chemical 

 energy, because the process of passing into a gas requires a certain amount of heat, and 

 consequently absorbs a certain amount of work. If gaseous hydrogen is produced, it 

 shows that there are already conditions sufficient for the transmission of heat to the 

 hydrogen evolved in order to convert it into a gas. It is evident at the moment of evo- 

 lution that heat, which would be latent in the gaseous hydrogen, is transmitted to its 

 molecules, and consequently they are in a state of potential, and can hence act on many 

 substances. 



Let us here remark the circumstance, which will be clearly understood from what has 

 been said above, that hydrogen condensed in the pores of certain metals, like palladium 

 and platinum, acts as a reducing agent on many substances. It will afterwards be 

 understood that substances containing much hydrogen, and easily parting with it, can 

 also act vigorously in effecting a reduction. 



VOL. I. L 



