316 CONSIDERATIONS ON ELECTRICITY. 



structing a battery of extraordinary intensity often take no consideration thereof, 

 and 3'et every elementary work on pliysics tells tliem that ''the intensity of an 

 electrical pair is directly proportional to its electro-motive force, and inversely to 

 the total resistance." 



Muriatic acid, chlorine dissolved in water, or a chloride, would be active agents 

 almost as energetic as sidphuric acid, but less" practical, with the exception of 

 common salt. Soda dissolved in water would act energetically upon zinc, but 

 the equivalent of electricity thereby generated would be very expensive. A 

 pair whose active element should l)e aluminum and a solution of soda would 

 possess very great energy, but would be truly an article of luxury. 



The controversy is greater when the choice of the depolarizing material and the 

 aiTangement of the pair is in question. A methodical study should not allow 

 itself to be misled, however great may be the combination ; the observer must 

 pay attention to the two essential elements, which most inventors neglect. "We 

 know the opposite influence of both the substances which surround the electrodes ; 

 we know, also, that the total electro-motive force is the sum of those which are 

 developed in the interior of the i)air between the ditierent elements of which it 

 consists ; the analysis must therefore be extended to these partial actions. Ac- 

 count must then be taken of the conductibility which is proper to the elements 

 themselves, and of the influence which their arrangement exerts on the resistance 

 of the pair. The electro-motive force is of course in each pair independent of 

 the disposition, the dimensions, and the nature of the diaphragms. 



The three other points to be considered in the arrangement of an electrical 

 battery, the choice of the positive electrode, the dividing walls, and the general 

 disposition of the pair, are exclusively dependent on the resistance which they 

 oppose to the conductibility. The positive electrode must be as perfect a con- 

 ductor as possible, and on this account the purest possible metal must be employed ; 

 to supply such, however, is very costl3\ The use of platina has been renounced, 

 as it is mechanically wasted. For batteries of very energetic action, as those with 

 nitric acid, chlorides, &c., coke or retort coal would seem to be the only proper 

 conductor. But this substance, as furnished in trade, is found upon tiial to have 

 very different qualities. Some specimens resist fi-acture and conduct well, while 

 others are very porous and frangible, so that sometimes the elements of one and 

 the same battery differ greatly in the intensity. 



This inconvenience, which is founded on the inconstant nature of the positive 

 conductor, is diminished with elements of weaker intensity, where the deijolariz- 

 ing substance is a metallic salt, whether in solution or solid. Hero we may 

 plainly adopt the same metal which forms the base of the salt. The conducting 

 surface is then, through the action of the pair itself, always maintained in a state 

 of absolute purity. The constancy of the intensity of a pair results irom the 

 maintenance of a continual identity in the surfaces of both conductors. Much, 

 moreover, is gained in this way as regards expense, for it is the only means of 

 completely recovering the costly substance which is employed in the depolariza- 

 tion. Another inducement for adopting for the positive electrode the same metal 

 which is contained in the salt surrounding it results from a consideration already 

 presented. Since the total electro-motive force of the pair is the sum of those 

 forces which are developed in the different parts, it must be an object of interest 

 to limit that force which proceeds from the contact of the positive electrode, when 

 opposed to the principal intensity in consequence of the attack of the electro- 

 positive metal, and on the other hand to develop that which is similarly directed 

 with this intensity. The latter will generally be the case, if the neutral salt 

 and the metal are sufficiently pm-e. 



The choice of the depolarizing substance must be decided by the following 

 considerations : by its affinity for hydrogen, in order that it may be readily and 

 completely reduced ; by the nature and physical condition of the precipitated 

 metal, when it is a metallic salt, and by the chemical condition of the products 



