Page:Popular Science Monthly Volume 92.djvu/324

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SMALL manufacturing concern which uses a gas heated enameling oven, found that considerable gas was wasted because the workmen frequently forgot

to shut off the gas when quitting their work for the night. As a result, the oven burner would be left on all night, with the consequent waste of gas and the liability of overheating and setting fire to the building or of doing damage to the oven and its contents.

To prevent this, the shut off valve on the gas line was provided with an insulated extension on the valve handle, as shown in the illustration. Over the end of this insulated extension is placed a metal ferrule which closes the contact between the two metal contact pieces attached to the two wires when the gas is shut off. These two wires form one side of the circuit for the lamp located in the night watchman's office, so that the gas must be shut off before the lamp can be lit. Should the gas be left turned on after working hours, the watch-man is aware of the fact as soon as he comes on duty, as he can only secure light in his office when the gas is shut off from the oven burner. The diagram in the illustration shows the wiring scheme in which a snap switch is used to turn off light after the signal shows that the valve has been closed.

This signal, while especially built for this purpose, is only suggestive and may be used in many like places us a safety device that will always signal when a certain necessary piece of work must be done on a set time, which may otherwise be forgotten by a careless operator or watchman.—

ROCURE 1 lb. of chloride of zinc crystals, and dissolve them in about 1 quart of distilled water. Stir, until all the crystals pass into solution, adding more water if necessary. After all the crystals have dissolved, pour the solution into a clean vessel, and add enough distilled water to make up 2 quarts. Add 1 lb. of sal ammoniac to the solution, and stir it until the crystals have dissolved. Have a vessel ready to receive the contents. Then the prepared solution can be set aside for future use, after the vessel has been labeled "battery solution."

The cell is constructed, as shown in the accompanying illustration, from a zinc-lined can and blotting paper. Moisten the blotting-paper lining with the battery solution, and pour off all excess liquid. Permit the blotting paper to become almost dry. Mix finely powdered manganese and carbon with a small quantity of the battery solution until it has acquired the consistency of a stiff paste. Put the carbon center post in the can, after having covered the bottom of the can with a layer of sand about ¾-in. thick.

The can is then ready to receive

the paste, which should be packed down hard with an improvised ram. The top of the cell should be sealed with paraffin, or a similar substance that can be removed easily, in order that the cell may be renewed at any time with little or no trouble.—