10. Two-fluid Battery. Fig. 8. When two or more cells are joined together the combination is called a battery. Fig. 8 shows two experimental cells joined in series. (Study methods of joining cells.) For convenience, and to keep them from being easily overturned, a frame has been made for them. The base, B, is 8 × 4 × ⅞ in. To the back of this is nailed the upright board, A, 8 × 4½ × ½ in. On the top of A are 3 binding-posts, 1, 2, 3, which consist of metal strips 1¼ × ½ in. At the lower ends are screws which are connected with the cells, as shown. Spring binders can be easily slipped on and off the upper ends of the strips, so that one or two cells can be used at will. Bent strips, C, are nailed to B, to hold the tumblers firmly in place. This framework is not necessary, of course, to the proper working of the battery, but with it you are much less liable to upset the cells.
11. Gravity Cell. Fig. 9. In the two-fluid cell of [App. 7] the fluids were kept apart by the porous cup. The gravity cell is really a two-fluid cell in which the two liquids are kept separate by the joint action of the current and the force of gravity. This cell is used for telegraph lines and for other closed-circuit work.
12. Construction. The zinc and copper, Z and C, Fig. 9, can be purchased about as cheaply as you can make them. There are many forms of the zincs, the one shown being called the crow-foot shape. The copper may be star-shaped, or as shown. If you wish to make C, use thin sheet-copper. Brush copper, 1¾ in. wide, is excellent for the purpose. Use a piece 12 or 15 in. long, and fasten to one end of it a copper wire, W, which must be covered with paraffined paper, or with rubber or glass tubing, where it passes up through the zinc sulphate solution and near Z. The glass jar, J, may be made from a large glass bottle. (See index for battery jars.)
13. To Set Up the Cell. (A) Place C upon the bottom of J, with W in the position shown. (B) Put in enough copper sulphate crystals to cover the bottom of J, but do not try to entirely cover C. At the start ½ lb. will be enough. (C) Pour in clean water until J is half full. (D) In another vessel dissolve 1 or 2 oz. of zinc sulphate in enough water to complete filling, J. (E) Hang Z in place (Fig. 9). Z must never touch C. They should be about 3 in. apart. A wire is attached to Z by the screw, S, and the hole, H. (F) Pour the zinc sulphate solution into J until it is within an inch of the top. It should cover Z.
Fig. 9.
(G) Connect the wires leading from Z and C to your sounder and key. (See diagram.) The cell will be weak at first, and it may not be able to run your sounder. If this is the case, "short-circuit" it by allowing the current to run around and around through the sounder and key, the switch being closed. You may also "short-circuit" the cell by joining the two wires together. This will, in a few hours, make the dividing line between the blue and white quite distinct, when the cell will be stronger. If you have a short line only, the battery may be short-circuited through your sounder or other coils of wire for 5 or 6 hours a day, without working it too much. It may be necessary to draw off some of the clear zinc sulphate, replacing it with clear water, if the blue line gets too low. Add water occasionally to make up for evaporation.
14. Regulating. The two solutions are kept apart by gravity, as the copper sulphate is heavier than the zinc sulphate. The dividing line between the blue and white solutions is fairly clear when the battery works well, and it should be about half way between C and Z, or about at J, Fig. 9. Never allow the blue to get as high as Z, as this indicates that the cell is not worked enough. The dividing line can be lowered by allowing it to run a buzzer or bell for a few hours, or by simply short-circuiting it. If the blue gets much below J it indicates that you are working the cell too hard, or that you need more copper sulphate. The harder the cell works, the more zinc sulphate is formed, and the lower the dividing line becomes.