Chapter 1

CELLS AND BATTERIES.

APPARATUS 1.

_1. Carbon-Zinc Cell._ Fig. 1. If you have some rubber bands you can quickly make a cell out of rods of zinc and carbon. The rods are kept apart by putting a band, B, around each end of both rods. The bare wires are pinched under the upper bands. The whole is then bound together by means of the bands, A, and placed in a tumbler of fluid, as given in App. 15. This method does not make first-class connections between the wire and rods. (See Sec. 3.)

APPARATUS 2.

_2. Carbon-Zinc Cell._ Fig. 2. In case you want to make your cell out of carbon and zinc rods, and do not have any means of making holes for them in the wood, as in App. 3 and 4, you will find this method useful. Cut grooves, G, into one side of the wood, A, which should be about 4-1/2 x 1 x 1/2 in. The grooves should be quite deep, and so placed that the rods will be about 1/4 in. apart. A strip of tin, T, 1/2 in. wide, should be bent around each rod. The screw, S, put through the two thicknesses of tin will hold the rod in place. Another screw, X, acts as a binding-post. The zinc rod only is shown in Fig. 2. The carbon rod is arranged in the same way. Use the fluid of App. 15.

3. Note. When the bichromate solution of App. 15 is used for cells, the strong current is given, among other reasons, because the zinc is rapidly eaten up. This action goes on even when the circuit is broken, so always remove and wash the zinc as soon as you have finished.

APPARATUS 3.

_4. Carbon-Zinc Cell._ Fig. 3. The wooden cross-piece, A, is 4-1/2 x 1 x 1/2 in. The carbon and zinc rods, C and Z, are 4 in. long x 1/2 in. in diameter. The holes are bored, if you have a brace and bit, so that they are 3/4 in. apart, center to center. This makes the rods 1/4 in. apart. To make connections between the rods and outside wires, cut a shallow slot at the front side of each hole, so that you can put a narrow strip of tin or copper, B, in the hole by the side of each rod. Setscrews, S, screwed in the side of A, will hold the rods in place, and at the same time press the strips, B, against them. Connections can easily be made between wire and B by using a spring binding-post, D, or by fastening the wire direct to the strips, as shown in App. 4.

Use the battery fluid given in App. 15, and use a tumbler for the battery jar. This cell will run small, well-made motors, induction coils, etc. (See Sec. 3.)

APPARATUS 4.

_5. Carbon-Zinc Cell._ Fig. 4. The general construction of this cell is the same as that of App. 3. There are 2 carbons, C, each 4 x 1/2 in. The holes for these are bored in A 1-1/4 in. apart, center to center. The zinc rod, Z, is a regular battery zinc, 6 x 3/8 in., and has a binding-post, Y, of its own. The rods, C, are held in A, and connections are made as explained in App. 3.

The wire, X, is fastened direct to the strips, B, as shown. When ready to use this cell, be sure that the wire connecting the carbons does not touch Z. (Why?) The other wire is connected to Y. The wooden piece is 4-1/2 x 1 x 1/2 in. Use the battery fluid of App. 15 in a tumbler. This cell will run small motors, and is good for induction coils, etc. (See Sec. 3.)

APPARATUS 5.

_6. Experimental Cell._ Fig. 5. Cut a strip each of copper, C, and zinc, Z. (See list of materials.) They should be about 2 in. wide and 4 in. long. Punch a hole through each, one side of the center, for screws, E. The wooden cross-piece, A, should be 4-1/2 x 1 x 7/8 in. The battery-plates, or elements, should be screwed to this, taking care that the screws, E, do not touch each other. If the holes are made in the position shown in Fig. 5, the screws can be arranged some distance apart.

The wires leading from the cell may be fastened under the screws with copper burs, or spring binding-posts (App. 42) can be slipped on the top of the plates.

The solution to be used will depend upon what the cell is to do. For simple experiments use the dilute acid (App. 14). If for small motors, use the formula given in App. 15. The zinc should be well amalgamated. (App. 20.)

APPARATUS 6.

_7. Experimental Cell._ Fig. 6. In some experiments a comparison is made between cells with large plates and cells with small ones. This form will be convenient to use where narrow plates are desired. Those shown are 4 x 1/2 in. They are screwed to the cross-piece, which is 4-1/2 x 1 x 7/8 in. Do not let the screws touch each other. The wires are fastened under the screw-heads.

APPARATUS 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 x 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 x 2 in. The narrow strip, or leader, A, is 5 x 1/2 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 2-1/2 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.)

APPARATUS 8.

_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 x 4 x 7/8 in. To the back of this is nailed the upright board, A, 8 x 4-1/2 x 1/2 in. On the top of A are 3 binding-posts, 1, 2, 3, which consist of metal strips 1-1/4 x 1/2 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.

APPARATUS 9.

_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, 1-3/4 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 1/2 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.

(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.

15. Gravity Batteries of two more cells are needed when used on telegraph lines. You will need 1 cell to each sounder; that is, for a short line in the house with two sounders, use 2 cells. If you use a few hundred feet of wire running to a friend's house, use 3 cells. They must be joined in series; that is, the copper of one to the zinc of the other. (See diagram of complete telegraph line.) Do not use ground connections for short lines and home-made sounders; use a return wire. Do not use different kinds of cells upon the same line.

APPARATUS 10.

_16. Storage Battery._ To show the principle of storage batteries it is only necessary to use two plates of lead dipped in the battery fluid of App. 14. The cell may be made as in App. 5, Fig. 5, the only difference being that both plates are of sheet-lead. It will be an advantage to make the plates rough by hammering against them a coarse file. (See explanations and experiments with this form of cell in text-book.)

APPARATUS 11.

_17. Porous Cups for Two-fluid Cells._ Fig. 10. Very good porous cups can be made from ordinary blotting-papers, the average ones measuring 9-1/2 x 4 in. White ones should be used, so that you will not be bothered with the color coming out. Soak the edge along one end of the blotter in paraffine (Index) for about 1/4 in. When this is cold, roll the blotter into the form of a cylinder that is a little over 1 in. inside diameter, and have the paraffined end on the outside. This will make 2 thicknesses of paper all around, and a little to spare. Rub a hot nail over the paraffine to melt it, and stick the end to the cylinder. By putting on a little more paraffine along the edge where the end laps over, a good solid cylinder can be made. The cylinder should be strengthened still more by dipping each end into melted paraffine for about 1/8 in. The dark stripes around the ends and down the front of the cylinder (Fig. 10) are to represent the paraffine. Cut out a bottom about 1/4 in. larger all around than the cylinder. This may be paraffined to make it stiff. It should be fastened to the cylinder with paraffine. Paraffine is not acted upon or softened by water or acid, as is the case with glue.

APPARATUS 12.

_18. Porous Cups for Two-fluid Cells._ Instead of the blotters of App. 11, you can use short lengths of mailing-tubes, which are used to protect pictures, etc., when sent by mail. If you find that the particular tube tends to unwind when soaked, you can use a little paraffine along the edges of the spiral, as suggested in App. 11. Bottoms can be made for the cups as before.

APPARATUS 13.

_19. Porous Cups for Two-fluid Cells._ Ordinary unglazed earthen flower-pots make good cups. The hole in the bottom should be closed with a cork, or by fastening a piece of pasteboard over the hole with paraffine. The pasteboard may be fastened to the under side of the bottom more easily than to the upper side.

20. Note. It is a good idea to soak the top edge of porous cups for about 1/4 in. in paraffine to keep the solutions from crawling up by capillary attraction. If the solutions constantly evaporate from the soaked tops of the cups, they not only waste but they get the whole thing covered with crystals.