Remarks on the Galvanic Battery. 145 



separated, provided the original plate has been properly 

 prepared by being oiled and black-beaded before being 

 used. The porous cell in which the zinc is placed should 

 have a capacity of at least 150 cubic inches. As the resist- 

 ance of large clay cells is more than three times as great 

 as for those made of leather, the latter are preferred ; since 

 with the same surface of zinc q. is nearly doubled. The 

 constant use of leather cells during the past year fully 

 demonstrates their superiority over those made of white 

 clay. For it is found in practice that for working magnets 

 such as are used in telegraph offices for local sounders, one 

 element as described above, gives more effective working 

 force than two of those in ordinary use. The zinc cast- 

 ing may be of any form; for cells of this size, it should 

 have an external surface of 50 square inches. 



The battery should be started with s. z. at 15° B. specific 

 gravity. Sulphuric acid should never be used in the cell 

 containing the zinc. Crystals of s. c. are suspended in a 

 bag or perforated cup near the top of the liquid sur- 

 rounding the negative plate, in order to keep the solution 

 at saturation. After a battery has been in constant use 

 for a number of months, crystals of s. c. will be found pre- 

 cipitated on the bottom of the jar. When this is the case 

 the liquid must be poured in another vessel, and all the s. 

 c. removed, as it seems to lessen q. During cold weather 

 the battery may be improved by adding occasionally a 

 little sulphuric acid to the s. c. solution. Between 40° and 

 100° Fahr., the specific resistance of the liquids is increased 

 about one-sixth for every 10° decrease of temperature. It 

 is not desirable therefore, to work the battery at a tempera- 

 ture below 50° Fahr. 



The zinc need not be amalgamated, but it should be 

 cleaned once in two or three months, and all the sediment 

 removed from the porous cell. 



[Trans. vi.~\ 19 



