378 EECENT PROGRESS IN PHYSICS. 



only embraces Davy's views, but goes still farther. It not only in- 

 cludes, under a common expression, tlie salts and the acids, but also 

 the oxides. In this relation it must be distinctly understood that, 

 while the type exists as a whole, and the replaceable metal is also 

 that which, as an element, may be separated from tlie type, it is by 

 no means necessary that the remaining elements should be, together, 

 capable of a separate existence. Before carrying out this theory in 

 its application to the phenomena of electrolysis, we should, as a bare 

 act of justice, state that it is mainly due to the labors of Laurent and 

 Gerhardt, chemists, who have gained the noble but uncoveted distinc- 

 tion that they have attained their greatest reputation when they 

 have — died. 



It is also not a little remarkable that the views of these chemists 

 should now be quoted as supporting a correct idea of electrolysis, 

 when their chief labor was to overthrow the so-called electro-chemical 

 theory. It is quite possible that some other generalization may cause 

 both theories to coincide, (a clue to which has been furnished by these 

 chemists ;) but, meanwhile, it is highly instructive to learn that 

 where the nature and reaction of various elements are concerned true 

 chemical philosophy is able to assert and maintain its own dominion. 



To proceed to details without entering into unnecessary refine- 

 ments, we shall show the electrolytic action upon the salt type, always 

 presupposing the indifference of either electrode to the substances 

 evolved, the metal (or the hydrogen) being eliminated at one pole and 

 the residue at the other, and no secondary eifect being produced. As 

 instances of the simplest case we have the following : 



From 0. H., II. is removed, and 0., the residue, is given off at the other pole. 

 From CI. H., H. is removed, and C!., the residue, is given off p.t the other pole. 

 From CI. Cu., Cu. is removed, and CI., the residue, is given off at the other pole. 



Of these water is the most stable compound, and is, therefore, de- 

 composed with the greatest difficulty. 



But, carrying out this view, such compounds as CI. Cu.g, &c., are 

 still considered as belonging to the same type ; but the metal is 

 regarded as entering into combination with a new equivalent, which 

 is either a simple multiple or fraction of that which usually occurs. 

 This hypothesis, advanced without reference to electrolysis, is strik- 

 ingly corroborated by the experiments of Becquerel, noticed further on. 



But if, with many chemists, we consider water to be Hj, the 

 ordinary oxides Mj, (and this is in accordance with the physical 

 properties of the elements,) we will have M H as a hydrated 

 oxide, which, in the case of K H, will be more readily decomposed 

 than water alone. 



In the instances above given we have noticed only such cases of the 

 saline type, which, on the abstraction of the metallic element, leave a 

 residue, itself an element and capable of a separate existence. But 

 in the " oxygen acids " the residue is not capable of a separate exist- 

 ence and breaks up into such compounds, or compounds and elements, 

 as can exist. As representatives of this class we have S 0^ H, or 

 generally S O4 M, from which H or M being taken, the residue 

 cannot remain as such, but is given off and S O3 unites with water 



