Page:Popular Science Monthly Volume 89.djvu/290

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A Home-Made Edison Battery

��THE good points of the Edison battery are great constancy, very low internal resistance and freedom from local action when on open-circuit. Following are the particulars of a home- made Edison battery which can be built very cheaply and which will give every satisfaction.

The battery consists of a perforated copper pipe A (Fig. i), containing black oxide of copper as the positive element, and a zinc cylinder C as the negative element.

The exciting liquid is a 25- per cent solution of caustic potash in water, which means a solution of one pound of caustic potash to three pounds of water. The containing jar is represented by D; E is a cover which excludes dust and from which the copper pipe and zinc cylinder are sus- pended by means of the brackets F and G. The two binding posts H are con- nected to A and C respectively.

The battery here described, which will give a constant current of 20 amperes, uses a containing- jar 6 ins. by 10 ins. In build- ing this battery it will be best to obtain the containing jars first, since all the other di- / / /!_ mensions are fixed by the size of the jar.

First procure a copper tube of 3-in. bore and 834 ins. long, about 1/32 in. thick. To perforate the tube, slip it over a stick of wood a little smaller in diameter than the tube; punch the holes through with a |)unch or a nail. The holes shoulif be about 3/8 in. in diameter.

Cut a wooden disk 3 ins. in diameter and about '^s '"• thick. Drill a ]/i-w. tlrain-liole in it and soak it for about fifteen minutes in molten i)araffin wax. Tlien fix the disk with shellac solution in the bottom end of the copper tube.

Procure some coi)per strip about I in. by y^ in. Bend 3 lugs, G, as shown, and rivet tluni to the cojjper cylinder. The

���Fig. 1. Dimen- sions and parts of the battery

���Fig. 2. Proper po- sition of the lugs on the cyHnders

��lugs must be equally spaced (Fig. 2), showing the drilling in the top cover E, where A' represents the holes for support- ing A , and Y the holes for supporting C. The copper cylinder is now completed and we take next the zinc cylinder in hand. This should be made from rolled zinc and not from cast ma- " terial. The best plan is to buy a cylinder of the size re- ([uircd as you are sure to get the right material. Prefera- bly the zinc should be well amalgamated as it lasts much longer. Three lugs made from the same strip as used f(3r the copper c\linfler should then be riveted to the zinc c\ Under. They must be again equally spaced as shown in Fig. 2.

One lug on each copper and zinc cylinder should then be soldered to the respective cylinder in addition to the riveting, so as to make as good a connection as possible. These two lugs are the ones subsequently connected with the l)inding posts H.

The cover E is now the last part to be made. It is made from good hardwood to the dimensions given and should be a snug fit in the containing jar. Six holes J^ in. in diameter are then drilled in the co\er and spaced as siiown in the figure, so as to avoid a short-circuit between the lugs (/ of the cojiper cylinder and till- lugs Fof the zinc cylinder. The cover must now be soaked in molten paraffin wax for at least fifteen minutes. Then ob- tain two large liinding posts H, ten 3/16-in. nuts, 6 washers for the same and 6 steel rods, screwed 3/16 in. f)n each end, one end to take the bind- ing posts or nut on top of the co\er E and the other end to take the nut below the brackets F and G.

In assembling the battery, first fill the copper c\'linder with black oxiile of copper and boll the cylinder to the co\er Fl. V\\ the zinc cNlinder C to the

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