CONSIDERATIONS ON ELECTRICITY. 315 



single pair, may determine in advance tbe electro-motive force of tlieir combina- 

 tion tlirongli the difference of the electro-motive forces of the metals which they 

 immerse in the selected liquid. 



The first part of the problem is therefore fixed ; inventors must, consequently, not 

 step be^'ond this narrow circle. The choice of the metal and the liquid depend 

 on the chemical operation upon one another, for thence results the electro-motive 

 force. Upon the question of practical economy it would be useless here to insist, 

 as the attention of the industrial inventor will of itself be sufficiently directed 

 to this point. 



The sources of a competent electro-motive force having been discovered, and 

 the degree of intensity determined, next arises the question of })ersistency. The 

 essential fact is here too easily forgotten, that the total intensity of a compound 

 pair is equal to the sum of the intensity of the chemical reaction of the liquid 

 on the electro-negative element, and of that of this liquid on the depolarizing 

 substance, while the total intensity of a single pair is equal to the difierence 

 between the intensity of the chemical activity and that which inversely proceeds 

 from the intensity determined through the polarizing current. So soon as the 

 inventor leaves out of consideration essential elements, chance alone can lead 

 Mm to a satisfactory solution. Whatever liqaid and metal be employed, there 

 always takes place a change of the latter, and a development of hydrogen gas 

 which collects about the positive electrode, whether this be metal or charcoal. 

 The inventor must therefore contrive that this gas shall be absorbed as com- 

 pletely and at as cheap a rate as possible. Acids, oxygen, salts, and combina- 

 tions of chlorine have hitherto been alone used. 



The question as to what active metal should be employed in electrical batteries, 

 is already well nigh exhausted. Only inventors entirely ignorant of the grounds 

 of its preference seek to replace zinc by some cheaper metal in order to obtain 

 an equivalent amount of electro-motive force. Some have had recourse to the 

 alloys, but they have not paid sufficient attention to the secondary currents, 

 which nevertheless play so considerable a part in the action of an electrical bat- 

 tery. On this account even iron and lead, which their comparative cheapness 

 seems so strongly to recommend, can be no substitute for zinc ; for by reason of 

 the variable contents of foreign admixtures it would be impossible to count upon 

 uniform electrical intensities. If it be true that the electrical function of quick- 

 silver in the amalgam of zinc is not known, 3'et its influence cannot be denied ; 

 but it must not be supposed that this resource is applicable to iron, tin, or lead, 

 for these metals are still less adapted to amalgamation. The value of their 

 electro-motive force, when brought into contact with diluted sulphuric acid, refers 

 itself to tests which are as chemically pure as possible. 



The chemists are at present engaged in researches for the discovery of new 

 metals, but they have as yet found only metals of alkalies or alkaline earths, of 

 which it would seem almost impossible that large masses should be furnished. 

 So soon as these metals shall have jjassed into the service of practical industry, 

 as is already the case with sodium, aluminum, and magnesium, there is reason 

 to hope that an electro-positive element for the electric battery will be discov- 

 ered, w'hich shall 1)0 as potent as zinc. The so-called spectroscopic metals will 

 in this respect probably be not far removed from potassium and sodium. 



The choice of the liquid does not absolutely depend on that of the metal which 

 forms the electro-positive element ; we must here keep in view also the duration 

 of the action of the battery and the chemical nature of the depolarizing sub- 

 stance. If only the energy be regarded and the duration of action be limited, 

 the intensity of chemical activity is of greatest interest ; for amalgamated zinc, 

 diluted sulphuric acid, is then preferably as the active liquid. It is not unimportant 

 here to remark that the electro-motive force is not increased with the degree of 

 strength of the acid. Electro-motive force and resistance are words only too 

 often used without being sufficiently comprehended. Inventors who aim at con- 



