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battery was shown by its fusing a steel wire, which Grove's 

 only raised to a dull red heat. I have been told by persons 

 who tried the two batteries, that they found the heating power 

 of the cast-iron battery to be twice as great as that of Grove's. 



♦' The decomposing powers of the two batteries were com- 

 pared by the quantities of the mixed gases which they pro- 

 duced during the space of three minutes. The result clearly 

 established the superiority of the cast-iron battery. 



" I have tried various kinds of cast iron, and have found 

 them all to possess nearly equal power. I have got cast iron 

 plates containing oxide of chromium: they did not appear to 

 have any advantage over common cast iron. Perhaps, by 

 mixing with cast iron some of the more negative elements, 

 an increase of power may be obtained. 



" Soon after I had discovered the great electromotive 

 power of platinized lead and cast iron, when excited by nitric 

 or nitro-sulphuric acid, I proposed to the Trustees of the Col- 

 lege to change our Wollaston batteries into a platinized lead 

 or cast iron one. They readily authorized me to expend the 

 sum required for the change. After weighing well the relative 

 advantages of platinized lead and cast iron, I resolved on the 

 latter, principally because I found that it did not require to be 

 platinized. In one of our Wollaston batteries there were 300 

 zinc plates, each four inches square, and in the other twenty 

 plates, each two feet square. In the two batteries the surface 

 of the zinc plates was something more than 113 square feet ; 

 the copper surface was twice as great as the zinc surface. 

 After mature reflection on the best form for the new battery, 

 and on the most convenient size of the zinc plates, I resolved 

 to get water-tight, cast-iron cells, rather than plates; to retain 

 the 300 four-inch plates; and to divide the twenty large plates 

 into 320 small ones, each six inches square. I therefore or- 

 dered 300 porous cells, each four and a half inches high, four 

 and a half inches broad, and half an inch wide, for the four- 

 inch plates; and 320 porous cells, each six and a half inches 



