28 PRINCIPLES OF CHEMISTRY 



formed into others. Therefore the identification of clu inical force with 

 electricity will not bear experimental proof. 30 As of all the (mole- 

 cular) phenomena of nature which act on substances at immeasurably 

 small distances, the phenomena of heat are at present the best (com- 

 paratively) known, having been reduced to the simplest fundamental 

 principles of mechanics (of energy, equilibrium, and movement), which, 

 since Newton, have been subjected to strict mathematical analysis, 

 it is quite natural that an effort, which has been particularly 

 pronounced during recent years, should have been made to bring 

 chemical phenomena into strict correlation with, and under the theory 

 founded on, the already investigated phenomena of heat, without, how- 

 ever, aiming at any identification of chemical with heat phenomena. 

 The true nature of chemical force is still a secret to us, just as is the 

 nature of the universal force of gravity, and yet without knowing what 

 gravity really is, by applying mechanical conceptions, astronomical 

 phenomena have been subjected not only to exact generalisation but to 

 the detailed prediction of a number of particular facts ; and so, also, 

 although the true nature of chemical affinity may be unknown, there 

 is reason to hope for considerable progress in chemical science by 

 applying the laws of mechanics to chemical phenomena by means of 

 the mechanical theory of heat. But as yet this portion of chemistry 

 has been but little worked at, and therefore, while forming a current 

 problem of the science, it is treated more fully in that particular 



50 Especially conclusive are those cases of so-called metalepsis (Dumas, Laurent). 

 Chlorine, in combining with hydrogen, forms a very stable substance, called ' hydrochloric 

 acid,' which is split up by the action of an electrical current into chlorine and hydrogen, 

 the chlorine appearing at the positive and the hydrogen at the negative pole. From this 

 electro-chemists considered hydrogen to be an electro-positive and chlorine an electro- 

 negative element, and that they are held together in virtue of their opposite electric 

 charges. It appears, however, from metalepsis, that chlorine can replace hydrogen (and 

 reversely hydrogen replaces chlorine) in its compounds without in any way changing the 

 grouping of the other elements, or altering their chief chemical properties. Thus the 

 capacity of acetic acid to form salts is not altered by replacing its hydrogen by chlorine. 

 Here an electro-positive element is replaced by an electro-negative element, which is 

 quite contrary to the electrical theory of the origin of chemical attraction, which has thus 

 been entirely overthrown by the facts of metalepsis. We must remark, whilst consider- 

 ing this subject, that the explanation suggesting electricity as the origin of chemical 

 phenomena is unsound in that it strives to explain one class of phenomena whose nature 

 is almost unknown by another class which is no better known. It is most instructive to 

 remark that together with the electrical theory of chemical attraction there arose and 

 survives a view which explains the galvanic current as being a transference of chemical 

 action through the circuit i.e., regards the origin of electricity as being a chemical one. It 

 is evident that the connection is very intimate, but both kinds of phenomena are indepen- 

 dent and represent different forms of molecular (atomic) movement, whose real nature is 

 not yet understood. Nevertheless, the connection between the phenomena of both cate- 

 gories is not only in itself very instructive, but it extends the applicability of the general 

 idea of the unity of the forces of nature, conviction of the truth of which has held so 

 important a place in the science of the last ten years. 



