50 The Rev. Dr. Callan on the Construction and Power 



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 College 

 to change our Wollaston batteries into a platinized lead or 

 cast iron one. They readily authorised 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 20 

 plates, each 2 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 4-inch plates; and to divide the 20 large plates into 

 320 small ones, each 6 inches square. I therefore ordered 

 300 porous cells, each 4| inches high, 4A inches broad, and 

 \ an inch wide, for the 4-inch plates; and 320 porous cells, 

 each 6~ inches high, 6| broad, and about an inch wide, for 

 the 6-inch plates. I also ordered 300 cast-iron, water-tight 

 cells, each about 4^ inches high, .5 inches broad, and an inch 

 wide, to hold the small porous cells ; and 320 cast-iron cells, 

 each about 6^ inches high, 7^ broad, and If wide, to contain 

 the large porous cells. The new battery then was to consist 

 of 620 voltaic circles, in which the entire zinc surface would 

 be 113 square feet, and the surface of cast iron would exceed 

 226 square feet; but on account of several disappointments 

 I have been obliged to be content for the present with 577 

 voltaic circles, containing 96 square feet of zinc, and about 

 200 square feet of cast iron. In this battery, which was ex- 

 hibited in the College on the 7th of the last month, there were 



