OF DENISON UNIVERSITY. 
21 
the voltaic cell. It consists of a small slip of sheet zinc, one centi- 
metre wide and six long, a similar slip of sheet copper a little longer, 
held by two saw cuts across the edge of a piece of thin board two 
c.m. wide, ten long and one thick, as shown in the figure. Two sim- 
ilar couples should be prepared, one with zinc amalgamated, the other 
without. The upper extremities of the slips should be filed flat and 
kept bright, so that good electrical contact can be secured between 
them, by simply laying a little slip of sheet copper d, across the tops. 
In use the metals are immersed in a flat cell containing dilute sulphur- 
ic acid and projected with a lantern or porte-lumiere. The following 
are among the points that the couple is designed to illustrate : 
a. The fact that although the hydrogen is given off at the copper 
plate, the action is really at the surface of the zinc. This is shown 
very prettily by the currents of zinc sulphate solution falling from the 
zinc. These currents are clearly seen by virtue of their high refractive 
power. 
b. The effect of amalgamation. This is very satisfactorily de- 
monstrated by comparing the appearance of a couple having its zinc 
amalgamated with that of a couple having its zinc unamalgamated. 
A good idea of the relative amounts of local and useful action may be 
gained by comparing the rates of evolution of hydrogen at the zinc 
and copper plates respectively. 
c. Diminished battery action with increase of external resistance. 
This is shown by replacing the connecting slip by a little piece of 
gas carbon or thin platinum wire. 
d. The effect of a depolarizing substance is shown by using fresh 
bichromate battery solution in place of the dilute acid. The non-ap- 
pearance of hydrogen and the change in color of the liquid from 
orange to green, are the points to be noted. If the glass cell is divided 
into two parts by a thin partition of plaster of paris, so that the- zinc 
may be on one side and the copper on the other, the complete action of 
any* two-fluid cell, as the Daniel, may be shown. 
e. Fig. 7 shows a couple in which the copper plate is fused into 
a small test tube so that currents may be compared quantitatively by 
the amounts of hydrogen which they liberate at the negative plate. 
A. D. Cole., 
