358 TENTH ANNUAL REPORT OP 



Callan constructed a zinc and iron Lattery, (Dingler's Journal, 

 vol. 109, p. 432 ; Philos. Mag., July, 1848, p. 49,) of a form simi- 

 lar to that which Grove had originally given to his zinc and platinum 

 battery, viz: rectangular smooth earthen cells^ 4i inches long and 4| 

 high. 



A turkey-cock was instantly killed by the stroke of such a battery, 

 composed of 620 elements ; and, on examination, the craw was found 

 burst. 



Callan says this battery acts fifteen times as strong as one of Wol- 

 laston's of the same size, and 1| as strong as an equally large Grove's 

 battery. This estimate seems exceedingly loose ; no facts, no meas- 

 urements are given, from which the constants of this battery can be 

 computed, even approximately ; without this knowledge a correct 

 valuation of a galvanic combination cannot be made. 



Measurements of the zinc and iron battery maybe found in the 81st 

 volume of Dingler's Journal, p. 2*73. 



Poggendorflf found for the electro-motive force of different combina- 

 tions the following values : 



Zinc and platinum ,,,,, 100 



Zinc and iron 78. 6 



Zinc and steel , 87.0 



Zinc and cast-iron 89. G 



The zinc being in dilute sulphuric acid, and the platinum, iron, &c., 

 in concentrated nitric acid. The resistances are tolerably equal in all 

 these combinations. 



§ 21. The iron and iron hattery. — That instead of the platinum 

 in Grove's battery, iron can be successfully substituted, is owing, no 

 doubt, to the fact that iron immersed in concentrated nitric acid 

 becomes passive, and in this state acts like a strong electro-negative 

 metal. From this Wohler and Weber inferred that iron, placed in 

 concentrated nitric acid, might act towards iron in dilute sulphuric 

 acid as platinum docs towards zinc. Their expectation was entirely 

 confirmed on trial, and they constructed a very powerful battery in 

 this manner. 



They found it advantageous to use ordinary tin-plate iron for the 

 metal immersed in the dilute sulphuric acid. 



Schunbein, also, by his researches on the passivity of this metal, 

 was led to the construction of a battery of passive and active iron. 

 (Dingler's Journal, vol. 84, p. 385.) 



The most convenient form of the iron battery is perhaps the follow- 

 ing : A cast-iron vessel receives the nitric acid and the earthen cell, 

 in which the dilute sulphuric acid is placed with the active iron. 



The rusting of the part of the iron vessel extending beyond the 

 liquid acts injuriously on the working of the battery. 



