78 The Rev. Dr. Callan's Experiments on the 



the hole in the brass screwed into the top iron plate. By means 

 of four |-inch bolts of iron, which pass through the top and bot- 

 tom iron plates, the top plate is screwed down on the India-rubber 

 collar. The wire is then wedged against the side of the hole in 

 the piece of brass, and the brass cap is screwed on. The board 

 between the bottom of the vessel and under iron plate, and the 

 India-rubber collar between the top and upper iron plate, insu- 

 late both plates from the iron vessel. The outside of the vessel 

 is connected with one end of the battery, and the top or bottom 

 plate with the other. Thus the two electrodes are connected 

 with opposite ends of the battery ; and if acidulated water, or 

 water containing any of the alkalies, be poured into the vessel, 

 it will be decomposed by the voltaic current. If a stopcock to 

 which a jet is attached be screwed to the top plate, the gases 

 will rush through the jet and may be ignited without the small- 

 est danger, for the explosion of the gases contained within can 

 never burst a vessel of such strength. I have had frequent 

 explosions without producing any injurious effect, though the 

 vessel was sometimes nearly half-filled with the mixed gases. 

 Before discarding the glass vessel, I began to use sheet ii'on in- 

 stead of platina electrodes. I found that when the intensity of 

 the battery exceeded that of three or four cells, the power of the 

 battery was soon exhausted ; hence in using a battery of eighty 

 cells, I was obliged to arrange them in twenty rows, each con- 

 taining four cells, and to connect all the end zinc plates so as to 

 form one, and all the iron cells at the other end so as to act as 

 one. I also found, that, to obtain the full effect of the decom- 

 posing power of the battery, the acting sm-face of each electrode 

 should be as large and a half as the acting surface of the zinc 

 in each circle. Hence about 9 square feet of sheet platina, 

 which would cost nearly 30/., are necessary for a voltameter 

 large enough for a battery of eighty 4-inch plates, when they 

 are properly arranged for decomposition. Platina plates are not 

 only very expensive, but they are also very easily torn and ren- 

 dered unfit for use. I used a pair of sheet-iron plates about 4 

 feet long and 9 inches broad. To one of them I soldered a piece 

 of thick sheet copper, and to the other a thick copper wire. I 

 then covered one of them with linen, and rolled the two into a 

 coil about !• inches in diameter. I had then two plates of iron, 

 nearly 3 square feet in surface, separated from each other by the 

 interposed linen. The coil was put into the iron vessel. The 

 copper plate soldered to one of the iron plates was connected 

 with the inside of the vessel, and the copper wire attached to 

 the other was connected with the perforated brass in the top. 

 The vessel was then filled with a solution of carbonate of potash. 

 I employed this solution in order to prevent the oxygen from 



