OF DENISON UNIVERSITY. 2 1 



the voltaic cell. It consists of a small slip of sheet zinc, one centi- 

 metre wide and six long, a similar slip of sheet copj^er a little longer, 

 held by two saw cuts across the edge of a piece of thin board </, two 

 cm. 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 to|>s. 

 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 copjjcr 

 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 pu. .- 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 licpiid from 

 orange to green, are the points to be noted. If the glass cell is divided 

 into two parts by a thin ])artition of ])laster of i)aris, 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. Fi!^. 7 shows a couj)le in which the c()j)i)er i)late is fused into 

 a small test tube so that currents may be comi)ared (piantitatively by 

 the amounts of hydrogen which they liberate at the negative |)late. 



.\. D. ('<»IK. 



