Page:Popular Science Monthly Volume 91.djvu/164

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��Popular Science Monthly

��fastening it to the shaft. The balance wheel may be made to suit the fancy of the builder.

Before assembling the parts, a commuta- tor must be made and slipped on the shaft back of the standard or between the up- right and end support. As it is necessary to have a break in the current for a short

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INSIDE ENDS TO OPPOSITE SOLDERED BINDING POST AND BRUSH The parts and their assembly for the construction of the universal motor

period a part of the commutator must be insulated from the shaft. This is ac- complished by making a base G cut from a hard fiber rod which is drilled to slip in the shaft. A brass tube having an inside diameter to fit on the fiber rod is filed as shown at H, and when assembled it appears as shown in the illustration on page 147.

The brush-holder for making contact on the commutator is constructed as shown at J. The base is made of hard rubber, or fiber \}/<z in. long and % in. thick. One end is rounded and drilled to slip over the core or lower bolt between the standard D and the magnet end C. The thin brass spring makes contact with the metal strips on the commutator as it revolves.

Both inside and outside ends of each coil are brought down through the base in rubber tubes. The inside ends of coils are soldered together. One outside end is connected with the iron standard D, and the other outside end with a binding post. The remaining binding post is connected with the spring on the brush-holder. — W. E. Day.

��Rebuilding Worn-Out Dry Battery Cells

THE most difficult part of rebuilding dry cells in quantity is the removal of the contents, which consists of peroxide of manganese and carbon powder tightly compressed and covered with pitch. Strike the pitch a sharp blow with a hammer to break it; then dig it out with a pointed tool like that of a screwdriver. Save the pitch and sand in separate receptacles.

The compressed oxide and carbon are also difficult to remove. About the only quick method is to use a twist drill Y% m - in diameter, placed in the chuck of a lathe. By pressing the zinc-cylinder of the cell on the drill and boring several holes in the compressed material to within 34 m - of the bottom, you will break it up so that all of the compound can be readily removed. Save the borings and the crumbled mass. If a small portion is left at the bottom it may be easily removed with the aid of a screwdriver. The material removed is spread out to dry and any lumps found are crushed. The exposure of this material in a thin layer not only permits the moisture to evaporate, but brings about a certain amount of reoxidation of the spent manganese dioxide. As soon as the ma- terial has become dry it must be heated to a moderate temperature — about 400 deg. F. will answer, but not to a bright red, as this will drive off some of the oxygen, every bit of which is needed in the renewed cell to act as a depolarizer. During the heating, which may be readily done in a stout iron pan, it must be well stirred. This process will eliminate a very large part of the exciting salts used in the original cell. The heated material must then be spread out and exposed to the air to cool. When cold it is ready to be mixed with the exciting salts and repacked in the original zinc-cylinders.

Almost all the cylinders may be used again after being soaked with hot water for about I hour or more. The soaking will loosen the original paper lining and it can be easily removed with a pointed tool inserted between the cylinder and the lining. Finally clean out the interior with a stiff brush and wet sand, or with a wire brush. When the cylinders are aired they are ready for re-filling. Some of the cylinders will be used up and unfit for use again. These may be dissolved in hydro- chloric acid to form a strong solution of

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