Fluid Galvanic Battery. 271 



tion of sulphate of copper, a copper plate 4 inches square, and a 

 zinc plate into a porous cell filled with dilute acid. When the 

 porous cell was put into the solution of sulphate of copper, and 

 the two metals connected with the opposite ends of the coil of 

 the galvanometer, a steady deflection of 25" was produced. The 

 copper plate was removed and a cast-iron one of the same size was 

 put in its place. The cast iron and zinc plate produced a deflec- 

 tion of 30 . Hence by substituting cast iron for the copper used 

 in Daniell's battery, a more powerful constant battery may be 

 made. The cast iron may be in the form of cells, which will act 

 as the negative metal, and will at the same time hold the solu- 

 tion of sulphate of copper. Thus the expense of glazed cells, 

 which are so easdy broken, may be saved. 



I have also tried cast iron excited with a solution of sulphate 

 of iron and zinc excited with dilate acid, both being separated 

 by a porous cell. A 4- inch cast-iron plate gave a deflection of 

 about 21°, whilst a Daniell's of the same size produced a deflec- 

 tion of 25°. Hence a battery nearly equal in power to Daniell's 

 may be made by exciting cast iron with sulphate of iron and ziuc 

 with dilute acid. The cost of sulphate of iron is only about the 

 eighth of that of sulphate of copper. 



Maynooth College, 

 March 1. 1855. 



P.S. I have lately tried a battery of 70 4-inch cells, in which 

 the zinc and cast iron were very near to each other. The battery 

 was charged with one part of sulphuric acid and three of a solu- 

 tion of common salt. The experiments consisted in the ignition 

 of metals and coke-points. A brass wire i of an inch diameter, 

 and a piece of zinc about f by i of an inch thick, were burnt 

 away so rapidly that the lecture room, which is about 40 feet 

 square and 18 high, was soon filled with the smoke produced 

 by the combustion of the metals. 



For the coke light, I used Deleuil's apparatus ; the light was 

 sufficiently intense to enable a person to read the smallest print 

 at the most distant part of the room whilst the window-shutters 

 were closed. During the entire time of the experiments, which 

 la-ted nearly an hour and a half, the action of the battery was 

 not suspended for more than about five minutes. At the end of 

 tin- experiments, the light appeared to be as brilliant as at the 

 Commencement, Had (here been time to continue the experi- 

 the power of the battery, would, I think, have been suffi- 

 cient to produce a strong coke light for another hour or half-hour, 

 i it of the acid used in charging the 70 cells was about 97. 

 or 107. 



The voltaic current by which the metals and coke points were 



