57 
ELECTRIC DISCHARGE WITH THE CHLORIDE OE SILVER BATTERY. 
Another comparison with 20 cells gave a value of 1'002 volt, II. ; a comparison made 
by Dr. Muirhead in 1875, gave T031 volt, III. 
Electro-motive force of the chloride of silver cell is consequently : 
volt. 
1 1-059 
II 1-002 
III 1-031 
Mean P03 
In all succeeding calculations we have taken the electro-motive force as — 
1-03 volt = i-- 3 X — 8 = -00343 electro-static unit. 
3 X 10 10 
The internal resistance of the battery depends partly on the distance between 
the zinc rod and the chloride of silver, but mainly upon the circumstance of the 
chloride of silver being used in the form of powder or fused into rods ; we have 
3240 powder-cells and 4800 rod-cells in work; gradually and after many months the 
internal resistance increases in consequence of a hard skin of oxychloride of zinc 
forming on the zinc rods. We have taken 5 ohms for the internal resistance of the 
rod, and 15 ohms as that of the powder-cells in the succeeding calculations. 
We have determined the electro -motive force of the two other haloid compounds 
of silver, and find it to be as under for the three haloids — 
volt. 
Chloride of silver . . .1*03 
Bromide „ . . . 0"908 
Iodide . „ ... 0*758 
To measure the striking distance at ordinary atmospheric pressures, we have used 
the discharger figured below, which was made from our drawings by our assistant, 
Mr. James En am, who has aided us materially during this investigation by his 
intelligent interpretation of our wishes, and his mechanical skill in carrying them out. 
The frame work is of ebonite, and its construction sufficiently obvious ; the screw S 
having a -^-th of-an-inch thread, has a cylindrical recess at the lower end into which 
is inserted one of the terminals to be used in the experiments (in this case a point 
P) ; the end of the screw has four slits cut through it, in order that it may be 
contracted and made to pinch tightly any terminal inserted in it by means of the 
binding-nut N, working on the end of the screw, which is slightly conical but still 
has a full thread cut upon it. The nut fixed in the cross head at the top of the 
frame through which the screw works is in metallic communication with the clamp C, 
and is divided horizontally into two parts which are pressed asunder by three spiral 
springs in order to prevent shake or play of the micrometer screw. At the base of the 
MDCCCLXXVIII. 
i 
