268 The Rev. Prof. Callan on a New Single 



iron cell excited by one part of sulphuric acid and two of water, 

 whilst it is coated with nitrate of iron, is considerably less than 

 one-half that of the current produced by the same cell excited 

 by the same fluid after the nitrate of iron has been removed. It 

 is necessary to clean the cast-iron cells or plates before they are 

 used, by leaving them for some time in dilute sulphuric or mu- 

 riatic acid. 



In the beginning of September I showed in the College a bat- 

 tery of 182 cast-iron cells excited by one part of sulphuric acid 

 and three of a strong solution of common salt. The experiments 

 made with this battery cousisted in the ignition of coke-points 

 and of various metals. A scientific friend who came from Dub- 

 lin to be present at the experiments, who had great experience 

 of the working of nitric acid batteries, and witnessed in the Col- 

 lege the action of 275 4-inch cells of the nitric acid battery on 

 one occasion, and of 200 cells on another, stated that the 182 

 cells of the single fluid battery appeared to him to be superior in 

 power to the 275 or the 200 nitric acid cells. On this occasion 

 I requested several persons to compare the degree of ignition 

 and illumination of the negative and positive coke-poiuts. In 

 order to be able to look steadily at the ignited points, they 

 used deeply-colom'ed glasses. They all stated that they could 

 not perceive any difference between the degree of ignition of one 

 point and the other. "When the connexion with the battery was 

 broken, both points appeared equally heated, and equally or 

 nearly equally consumed. 



It has occurred to me, that the superior heat and light of the 

 positive coke-point ignited by a nitric acid battery arise princi- 

 pally from the action of the exciting fluid on the positive metal ; 

 and that, because in the cast-iron battery excited by any of the 

 fluids I have used, the exciting fluid acts a good deal on the 

 negative as well as on the positive metal, the negative coke-point 

 should be ignited and illuminated nearly as much as the posi- 

 tive one. Perhaps also the galvanic power of the single fluid 

 cast-iron battery is proportional, not to the action on the zinc 

 alone, but to the sum of the actions on the cast iron and zinc. 

 If this be so, the expense arising from the consumption of metal 

 in producing a given galvanic power will be less in the single 

 fluid battery than in the nitric acid battery ; for zinc is more than 

 twice as dear as cast iron. 



In iising for the electric light a cast-iron battery of 60 cells, 

 excited by about one part of sulphuric acid, one of muriatic, and 

 two of water, I made an experiment which proves the great 

 intensity of this battery. After the battery had been at work 

 for about three-quarters of an hour, I emptied two of the cells 

 at one end. Whilst they were empty, the ends of the battery 



