Mr. G. W. Wigner on Grovels Battery. 449 



was found that when of the ordinary thickness they opposed a 

 serious resistance to the current. 



(3) The zinc and platinum were brought much nearer together, 

 thus diminishing the length of liquid through which the cur- 

 rent had to pass in each cell. In many cases the zinc plates 

 were put into absolute contact with the porous cell without any 

 apparent disadvantage. 



(4) A white porous cell of a very close and uniform texture 

 was at last selected, as embracing both the necessary conditions 

 of good conducting-power and pores sufficiently small to prevent 

 the free mixture of the acids. 



The second object sought was to prevent local action ; and this 

 was accomplished by putting a small quantity of mercury at the 

 bottom of each cell, in contact with the zinc, which was by this 

 means always thoroughly amalgamated. Ultimately the zincs 

 were made in two pieces — one flat piece 4 J X 3 for one side of the 

 cell, the other a bent piece to carry the platinum ; and the con- 

 nexion between the two pieces was formed t>y the mercury at the 

 bottom of the cell. This alteration was found to be a great con- 

 venience, as any zinc could be lifted out without disturbing the 

 adjoining cells. It also proved economical, the first cost of each 

 zinc being less and the durability greater; for the old shape 

 always broke at the lower bend long before they were worn out. 



Anothe source of loss still remained, in the short circuits 

 which were formed from one cell to another, and from the ter- 

 minals to the ground, by moisture and condensed acid, and 

 which, when working with 120 cells, were so strong as to render 

 it painful to touch the terminal screws of the battery while 

 standing on a stone floor. 



To obviate this, two glass rods about half an inch in diameter 

 were fixed lengthwise in the bottom of each tray, and on these rods 

 the cells stood ; thus any moisture which might condense settled 

 out of contact with the cells. The trays and small pieces of 

 wood which were inserted between each cell were of oak, baked 

 for twelve hours, and varnished with three coats of shell-lac var- 

 nish ; and when in use each tray (of ten cells) was insulated by 

 another series of glass rods ; so that the loss by local circuits was 

 reduced to a minimum. 



I have also found considerable advantage from working the 

 batteries in front of a large fire : the fumes of the acid are all 

 carried up the chimney, and condensation very greatly diminished. 



I next endeavoured to increase the constancy of the battery. 



The first step, of course, was to increase the dimensions of the 

 outer cells, to prevent the sulphuric acid from becoming so rapidly 

 saturated with zinc. I then tried the effect of stronger nitric 

 acid, even as high as 1*540 spec, grav., but eventually decided 



