250 REPORT—1896. 
tange of Resistance 
Aimpere-meter 
0O-Ol ampere. ° ° - . - 04 ~-onnr 
O-1 * 5 - : : . s “O08 Tras 
” . ' 2 - * -» 0;008. a 
O-100  ,, - ? ; 5 - 09-0008 ,, 
The ampere-mneter actually employed had a range of from 0-3-5 
amperes, the graduations corresponding to 0-02 of an ampere. The 
internal resistance was 0:03 ohm, and the readings above 0:1 ampere 
perfectly accurate and constant. For currents below 0:1 ampere an 
instrument with the range 0 to 0-1 ampere must be substituted, but such 
small currents are not required for the experiments described in this 
portion of the report. Small rheostats with mercury connections were used 
as resistances, one for each circuit, each having a series of resistance coils 
from 4 up to 40 ohms, and a total resistance of 80} ohms. 
The current density is in all cases calculated on 100 sq. cm. of cathode 
surface, and expressed as C.D. ; 9. 
Arrangement of the Circuits. 
The accompanying plans show the arrangement adopted for six circuits. 
The tables A and B are each divided into three parts by thin strips 
of wood, the current being carried in each case by wires from the brass 
terminals ‘}’ to the stand for the electrodes, which is placed between 
them. The circuit is completed or broken by an ordinary electric light 
switch, ‘8.’ 
The centre-table contains all the connections to the ampere-meter, 
voltmeter, and resistances, in addition to the instruments themselves, thus 
leaving the tables on which the analyses are carried out perfectly free ; 
this is a decided convenience. This centre-table is provided with a flap- 
cover, so that the instruments are protected, except when measurements 
are being taken. 
The details of the connections on the centre-table for three of the 
circuits are shown on Fig. 2. The board DD, which is fixed on to the 
centre-table, carries two small boards A’ and B’, fitted with mercury- 
cup connections ‘m’; it also carries three small blocks, C, on each of 
which are fixed three brass binding-screws, connected underneath by a 
broad copper strip. R,, R,, and R, are the resistance boxes. 
The negative wire from the secondary cells passes direct to the con- 
necting board C,, fixed on the wall at the back of the tables, the remaining 
wires from the batteries passing to the switch-board (Fig. 2), so that any 
number of cells from one up to six can be put into use. From the ter- 
minal of the switch-board a wire passes to the connecting board C,, and 
thence to the table A, where it is divided in parallel into the three circuits 
1, 2 and 3 by a small connecting board which, together with the necessary 
wiring, runs under the ledge of the table A (Fig. 1). The circuit is com- 
pleted from the connecting board C, through the mercury cup ‘m’ on the 
board A’ (Fig. 2), marked ‘to circuits.’ This cup is connected to the 
other cups 1, 2 and 3 on the same board by spanners of stout copper wire 
with ebonite handles. The resistance of the spanner is negligible, as is 
that of the ampere-meter, but in cases where that of the latter has to be 
considered, a spanner must be used, having an equivalent resistance. 
Similar spanners are used for the ampere-meter and voltmeter connections ; 
they are all of different lengths so as to prevent mistakes in taking 
measurements. Supposing the spanner be put to circuit No. 1, the cur- 
