Popular science monthly . st be very closely wound, in order toget it into the very limited space in thebottom of the mug. Before taking the coil from the block,rub into its surface a little asbestosretort cement, or a cement composed ofa mixture of silicate of soda and silica,or glass sand. This mixture, when dry,will tend to hold the coil together, andthe current may be passed through thecoil, to test it, as well as to bake it inits coiled shape. The support for thecoil is a disk made from a piece of5/i6-in. asbestos, wood or transite. Cutit to fit into the recessed part in thebottom of the
Popular science monthly . st be very closely wound, in order toget it into the very limited space in thebottom of the mug. Before taking the coil from the block,rub into its surface a little asbestosretort cement, or a cement composed ofa mixture of silicate of soda and silica,or glass sand. This mixture, when dry,will tend to hold the coil together, andthe current may be passed through thecoil, to test it, as well as to bake it inits coiled shape. The support for thecoil is a disk made from a piece of5/i6-in. asbestos, wood or transite. Cutit to fit into the recessed part in thebottom of the mug. Then with a chisel,remove enough material from the topof this disk to form a depression, 1/16 144 Popular Science Monthly in. deep, to receive the coil flush withits top. The leads of the coil are runthrough the disk. The surface of thecoil is then plastered evenly with retortcement. The legs are fastened to asecond piece of insulating materialwith round-headed brass machine-screws,)4 in. long, with nuts. See Fig. Cartridge shells make neat electricalcontacts for a rheostat Using Cartridge Shells forElectrical Contacts A NOVEL use for cartridge shells ofthe old center-fire kind, certainto interest the electrical experimenter,is in making rheostats, small switch-boards and important contacts on wire-less apparatus, where efficiency isconsidered. A hole a trifle smaller thanthe diameter of the shell is made in thebase and the cartridge shell forced intothe hole made, as shown in the proper wires are then soldered tothe metal on the inside, or the wire ma>be placed inside of the shell and heldsecurely in position by driving a woodenplug into the empty shell, as complete rheostat may be so heads of the shells ofi^er efficientcontacts. The Best Crystal Detectors IN spite of the fact that crystal detect-ors play so important a part in theexperimentation of electrical amateurs,their use is not understood as well as itshould be. There arc var
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectscience, bookyear1872
