Page:Popular Science Monthly Volume 88.djvu/497

 Popular Science Monthly

��469

��Reconstructing a Dry Battery

CONSTRUCTING or reconstructing a dry battery, if it is done care- fully and with pure materials, will pre- vent the unfortunate experience of the amateur experimenter, who upon buy- ing dry cells in an electrical store, finds they are old and that a generous por- tion of their strength has seeped out while lying on the shelves. So far as the cost of construction is concerned, a home-made dry battery is about as ex- pensive as a standard ready-made cell. The only gain is in the life and con- sistent ability of the battery.

The foundation of the home-made dry cell consists of the zinc cylinder, care- fully cleaned, from a worn-out battery. The cup should be boiled in clean water for several minutes. When the inner zinc surface is washed, it is lined with three or four layers of white blotting paper. This paper should be laid in firm- ly and held with clips but not glued. Two disks of blotting paper are placed in the bottom of the cup. Care should be taken that none of the inner surface of the zinc is exposed to the chemicals that are afterwards put in, or the life of the cell will be considerably shortened.

After blotting paper is in place, it should be soaked for several minutes in a solution of zinc chloride and sal am- moniac in distilled water. To arrive at the correct proportion of chemicals will take a little time unless a hydrometer is handy. The zinc chloride should be dis- solved first. Crystals should be dis- solved in the water until the hydrometer reading is 32 degrees. If a hydrometer is not available, a saturated solution of zinc chloride should be made; that is to say, a solution that has dissolved as much of the chemical as it is able. Add half again as much water as was originally used. This brings the solution to an approximate 32 degrees.

Powdered sal ammoniac should now be added until the solution is again sat- urated, when it is read\- for soaking tlic l)lotter lining of the zinc. The soaking process should continue until the blotter can absorb no more of the solution.

Chemicals with which the battery is filled consist of a thorough mixture of two parts of manganese powder and three parts of powdered carbon or

��graphite. Carbon is cheaper. Coke is still cheaper, although it does not an- swer the purpose quite so effectively. Retort carbon, or arc carbon, pulverized in an iron retort, can be used. The two powders can be thoroughly mixed if they are placed in a covered jar of some sort, and the jar rolled and shaken care- fully. Pains should be taken in mixing the powders, as a generous propor- tion of the bat- tery's future per- f o r m a n c e de- pends upon this operation. When the manganese and carbon pow- ders are thor- oughly inter- mingled, they are moistened w i t h the zinc chloride-sal am- moniac solution.

���Section through an ordi- nary dry cell

��Aloistening the powder does not mean bringing it to a pasty state. It should have a damp, lumpy appearance.

Tamping the mixture into the zinc shell is the next step, and it is the most important part of the process. After the

carbon rod is placed in the center, the pow- der should be dropped in, a little at a time, and tamped down forcibly w i t h a blunt stick and a ham- mer. It is a painstaking pro- cess, but the re- sults are worth the eft'ort. When the container is filled within about one-half inch from the top, the blotting paper layers are folded in- ward and the rest of the space filled with sealing wax or a mixture of par- affin and resin.

When the battery is finished, if the directions are carefully followed, it should give excellent results.

���Method of mixing ma- terials in a mortar

�� �