Radio broadcast .. (1922-30)

Record Details:

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240 Radio Broadcast tacked element before its efficiency, or current generating ability, is seriously impaired. In the dry cell, the outer zinc case (the element which decomposes) is only slightly eaten away before, the cell is rendered useless by either polarization or the drying up of the salt filling compound. If such a cell could be used until the zinc were totally destroyed, its life as a radio A battery would be prolonged many months. The making of a cell which will give a strong electric current until the zinc is considerably decomposed is neither difficult nor expensive. A set of six such cells, each giving about i.i volts, can be made at home for approximately the cost of four dry cells. The dry cells will give the same total voltage but have a much shorter life. Such a cell is that of which the Daniell battery is composed (a " battery" is merely two or more cells) and is easily made according to the following directions: FIG. 5 Molding the porous cup THE MATERIALS Six neckless quart jars Three ounces of mercury Four pounds of plaster of Paris Six sheets of zinc 7!" by 8" ' copper 3" by 6" Two pounds of copper sulphate Eight ounces of sulphuric acid The jars may be easily made by removing the necks from Mason or quart preserve jars. A line is scratched with a glass cutter around the shoulder of the jar. The scratch is then moderately heated over an alcohol or bunsen flame (Fig. 4) and the top of the jar immediately dipped into a pail of cold water. The shoulder of the jar should crack at the scratch and fall into the water, leaving a very satisfactory battery jar, such as is shown alongside the pail in Fig. 3. The porous cup of plaster of Paris is next made. A heavy paper cylinder with a bottom is formed for the outside of the mold. This, for the quart size jar, should be about 7" high and -2\" in diameter. A smaller tube, \\" in diameter, is also made. The plaster of Paris is mixed in a convenient bowl (mix, at a time, only as much as is immediately needed) to a paste-like consistency. This is poured into the large paper cylinder until the bottom is covered to a depth of one-half inch; -the smaller tube is now placed in the middle of the larger one, and the plaster of paris poured in between the walls until a complete cup is formed (Fig. 5), when it is permitted to harden. The zinc electrode (negative pole) is now prepared. The sheet is first thoroughly cleaned by wiping with a dilute solution of sulphuric acid. A drop of mercury (quicksilver) is then placed on the zinc and "rubbed in" with a piece of cotton moistened with the dilute acid. Both sides of the zinc are similarly treated, the coating of quicksilver forming an amalgamation with the zinc. The amalgamated zinc is rolled into a cylinder that will fit over the plaster of Paris cup, and a wire either soldered or bolted to one corner. The joint between the wire and the zinc should be coated with beeswax or vaseline. The positive pole or copper electrode is also a cylinder (or it may be merely a strip), but should be made smaller, so as to fit loosely within the porous cup. One quart of a saturated solution of copper sulphate should be made up. This is most easily accomplished by heating the water to just below the boiling point and dissolving in it, by vigorous stirring, all the copper sulphate crystals it will take up. Some of the blue crystals will be precipitated upon cooling, showing that the solution contains all that can be dissolved. The battery may now be assembled. The jar is half filled with water to which are added a few drops of sulphuric acid. Fig. 6 shows the