Fig. 7.
8. Experimental Two-fluid Cell. Fig. 7. This cell has a zinc strip, Z, and copper cylinder, C, for the "elements." The porous cup, P C, is fully described in [App. 11]. Z is 5 × 1 in., and should be well amalgamated ([App. 20]). (Study reasons for amalgamation.) A zinc rod, like that shown in Fig. 4, may be used instead of the strip. The copper cylinder, C, nearly surrounds P C, and is made from a piece of thin sheet-copper, 6 × 2 in. The narrow strip, or leader, A, is 5 × ½ in. To fasten it to C, punch two small holes in C and A, put short lengths of stout copper wire through the holes, and hammer them down so that they will act as rivets, R. C can be hung centrally in the tumbler by bending A as shown. Y and X are spring binding-posts ([App. 42]). The battery wires can be fastened directly to Z and A, as suggested in Fig. 4.
9. Setting up the Cell. Arrange as in Fig. 7, but remove Z from P C. Pour some of the acid solution of [App. 14] into P C until it stands about 2½ in. deep, and at once pour the copper solution of [App. 16] in the tumbler, on the outside of P C, until it stands at the same height as the liquid in P C. As soon as the liquids have soaked into P C, you can put Z in place, when the cell will be ready for use. Remove and wash Z, when you have finished, and if you wish to use this cell occasionally, remove the liquids and wash P C thoroughly in water. When dry it will be as good as new. The acid rapidly acts upon Z, so it is better to remove Z if you wish to leave the experimenting even for a few minutes only.
Put a few crystals of copper sulphate (blue vitriol) in the tumbler under the copper, to keep the copper solution saturated. (See text-book for the chemical action in this two-fluid cell.)
Fig. 8.