** To Use Old Battery Zincs [87]

When the lower half of a battery zinc becomes eaten away the remaining part can be used again by suspending it from a wire as shown in the cut.  Be sure and have a good connection at the zinc binding post and cover that with melted paraffin.  This prevents corrosion, which would otherwise occur from the action of the sal ammoniac or other chemical.  The wire may be held at the top by twisting it around a piece

[Illustration:  Showing Zinc Suspended]

of wood or by driving a peg through the hole in the porcelain insulator.  —­Contributed by Louis Lauderbach, Newark, N.J.

** Callers’ Approach Alarm [87]

This alarm rings so that callers approaching the door may be seen before they ring the bell and one can exercise his pleasure about admitting them.

If one has a wooden walk, the alarm is easy to fix up.  Take up about 5 ft. of the walk and nail it together so as to make a trapdoor that will work easily.  Place a small spring under one end to hold it up about 1/4 in. (A, Fig. 2).  Nail a strip of tin along the under side of the trap near the spring and fasten another strip on the baseboard, so that they will not touch, save when a weight is on the trap.  Connect up an electric bell, putting the batteries and bell anywhere desired, and using rubber-covered

[Illustration:  Alarm Rings When Caller Approaches]

wire outside the house, and the alarm is complete.

When a person approaching the house steps on the trap, the bell will ring and those in the house can see who it is before the door bell rings.  —­Contributed by R. S. Jackson, Minneapolis, Minn.

** Easy Method of Electroplating [88]

Before proceeding to electroplate with copper, silver or other metal, clean the articles thoroughly, as the least spot of grease or dirt will prevent

[Illustration:  Electroplating Apparatus]

the deposit from adhering.  Then polish the articles and rub them over with a cloth and fine pumice powder, to roughen the surface slightly.  Finally, to remove all traces of grease, dip the articles to be plated in a boiling potash solution made by dissolving 4 oz.  American ash in 1-1/2 pt. of water.  Do not touch the work with the hands again.  To avoid touching it, hang the articles on the wires, by which they are to be suspended in the plating bath, before dipping them in the potash solution; then hold them by the wires under running water for ten minutes to completely remove every trace of the potash.

For plating with copper prepare the following solution:  4 oz. copper sulphate dissolved in 12 oz. water; add strong ammonia solution until no more green crystals are precipitated.  Then add more ammonia and stir until the green crystals are re-dissolved giving an intense blue solution.  Add slowly a strong solution of potassium cyanide until the blue color disappears, leaving a clear solution; add potassium cyanide again, about one-fourth as much in bulk as used in the decolorizing process.  Then make the solution up to 2 qt. with water.  With an electric pressure of 3.5 to 4 volts, this will give an even deposit of copper on the article being plated.