THE SMITHSONIAN INSTITUTION. 359 



§ 22. Callan's zinc and lead hattery. — In the Pliilos. Ma^;. for 1847, 

 (sec. Ill, vol. XXXI, p. 81,) Callan describes a new voltaic combina- 

 tion, of wliicli Pog2:eudorff gave an account in volume LXXII of his 

 Ann., page 495. For tlie platinum of Grove's battery is here substi- 

 stituted platinised lead, which is immersed in a mixture of four parts 

 concentrated sulphuric acid, two parts nitric acid, and two parts of a 

 saturated solution of nitrate of potash. Tlie sine is in dilute sulphu- 

 ric acid, separated of course from the other liquids by an earthen cell. 



The action of this battery, according to Callan's account, is not in- 

 ferior to that of Grove's. 



Poggendorff found that in fact the electro-motive force of this combi- 

 nation was equal to that of Grove's ; and that the current from it for 

 many hours indicated the same constancy as that of a zinc and plati- 

 num battery. But, on the other hand, he found the addition of salt- 

 petre to the nitric acid no improvement, but the addition of concen- 

 trated sulphuric acid has the advantage of protecting the lead from 

 the action of nitric acid, which the pulverulent coating of platina 

 cannot do, and allows, besides, the use of dilute nitric acid. 



Considered strictly, this combination is a zinc and platinum battery, 

 since the lead serves properly only as a support for the thin film of 

 platinum ; therefore zinc and platinum are the terminations of the 

 metallic circuit immersed in the liquid. 



§ 23. The most convenient combination of a given number of voltaic 

 elements for obtaining the greatest effect vjith a giveii closing circuit. — 

 Theoretically, this subject has long since been settled, but the inves- 

 tigations are mostly conducted by the aid of the higher calculus, and 

 the whole is jiresented in such a form, that the practical use of the 

 proposition is indicated rather than iwWj exhibited ; on this account, 

 a somewhat more detailed exposition may here be in place. 



Generally, the question is stated thus : How should a given metal- 

 lic surface, which is to be used in constructing voltaic elements, be 

 arranged (that is, how many elements and how large should they bCj) 

 in order that a maximum effect shall be obtained with a 2;iven closing^ 

 circuit ? 



This form of the question does not correspond exactly with practical 

 cases. We are not required generally to construct the voltaic battery 

 for a given closing circuit ; but the question is, how to combine a dis- 

 posable number of galvanic elements to obtain a maximum effect. 



A maximum, strength of current may be obtained from a given number 

 of elements, if they be so arranged, that the resistance in the battery is 

 equal to the resistance in the dosing arc. 



I will first explain this proposition, then prove it, A given num- 

 ber of elements can be combined in the most varied manner. For in- 



