** How to Make an Electrolytic Rectifier [197]

[Illustration:  Electrolytic Rectifier and Connections]

Many devices which will change alternating current to a direct current have been put on the market, but probably there is not one of them which suits the amateur’s needs and pocketbook better than the electrolytic rectifier.

For the construction of such a rectifier four 2-qt. fruit jars are required.  In each place two electrodes, one of lead and one of aluminum.  The immersed surface of the aluminum should be about 15 sq. in. and the lead 24 sq. in.  The immersed surface of the lead being greater than that of the aluminum, the lead will have to be crimped as shown in Fig, 1.  In both Fig. 1 and 2, the lead is indicated by L and the aluminum by A.

The solution with which each jar is to be filled consists of the following: 

    Water 2 qt. 
    Sodium Carbonate 2 tablespoonfuls
    Alum 3 tablespoonfuls

Care should be taken to leave the connections made as shown in Fig. 2.  The alternating current comes in on the wires as shown, and the direct current is taken from the point indicated.

The capacity of this rectifier is from 3 to 5 amperes, which is sufficient for charging small storage batteries, running small motors and lighting small lamps.  —­Contributed by J. H. Crawford, Schenectady, N. Y.

** The Rolling Marble [197]

Take a marble and place it on a smooth surface, The top of a table will do.  Ask someone to cross their first and second fingers and place them on the marble as shown in the illustration.  Then have the person roll the marble about and at the same time close the eyes or look in another direction.  The person will imagine that there are two marbles instead of one.

[Illustration:  Rooling Marble]

** A Gas Cannon [197]

If you have a small cannon with a bore of 1 or 1-1/2 in., bore out the fuse hole large enough to tap and fit in a small sized spark plug such as used on a gasoline engine.  Fill the cannon with gas from a gas jet and then push a

[Illustration:  Gas Cannon Loaded]

cork in the bore close up to the spark plug.  Connect one of the wires from a battery to a spark coil and then to the spark plug.  Attach the other wire to the cannon near the spark plug.  Turn the switch to make a spark and a loud report will follow.  —­Contributed by Cyril Tegner, Cleveland, O.

** Old-Time Magic-Part VI [198]

** A Handkerchief Mended after Being Cut and Torn

Two persons are requested to come forward from the audience to hold the four corners of a handkerchief.  Then beg several other handkerchiefs from the audience and place them on the one held by the two persons.  When several handkerchiefs have been accumulated, have some one person draw out one from the bunch and examine for any marks that will determine that this handkerchief is the one to be mended after being mutilated.  He, as well as others, are to cut off pieces from this handkerchief and to finally tear it to pieces.