140 J{> murks cm tin Galvanic Battery. 



The use of a number of porous cells in the same jar. — Since 

 the decrease of 7. is due to the formation of s. z., the ques- 

 tion naturally arises, how can a battery be constructed that 

 will give a uniform current for a long period of time '.' 



The answer is plain, we must increase the capacity of 

 the cell in which the zinc is placed. 



In a two-gallon stone jar, three porous cells were placed 

 with a sheet of copper surrounding them. The current 

 was then passed through the galvanometer and rheostat, 

 and sufficient resistance inserted to make q. equal to that 

 due to single cell, when used alone. The amount of s. z. 

 formed in a given time was then measured, when it was 

 found each cell made as much s.z. as if only a single on.' 

 had been employed. This combination showed very great 

 local action. Nothing, therefore, would be gained by such 

 an arrangement, but on the contrary a much greater 

 amount of zinc would be consumed without advantage. 



We next had constructed large porous cells 6 inches in 

 diameter and 7 inches high having a capacity of 180 cubic 

 inches. Our previous experiments enable us to calculate 

 with considerable precision the length of time one of these 

 elements will maintain a maximum current of electricity. 

 Allowing 5-7 cubic inches for the amount of liquid satu- 

 rated daily between the limits 12° to 40°, it is apparent that 

 a battery of this size should remain constant for more than 

 30 days, without any external resistance being introduced 

 in the circuit. When electro-magnets are operated, as 

 tin' external resistance should at least be equal to that of 

 the battery, the current would remain constant for more 

 than two months on a continually closed circuit. 



The relation between ihe quantity of electricity and the specific 

 gravity of the sulphate of zinc. — Svanberg's experiments are 

 quoted by recent writers to prove that the electro-motive 

 force for Daniell's battery is not materially changed by the 

 nature of the liquid about the zinc. Although this state- 



