Page:Popular Science Monthly Volume 90.djvu/495

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Popular Science Monthly


��A New Mercury Interrupter for Spark Coils

THE distinctive feature of the break de- scribed below is its independence from the coil, the cooling of the mercury and the contact pieces and the use of water instead of magnetism to generate the im- pulses or vibrations. The drawings show the principle of the interrupter.

A glass tube A is closed at both ends by the stopper B, which supports a hard rubber tube C and a glass tube F.

A portion of the hard rubber tube C has been cut away as shown in the sketch and the end of the tube is closed by the plug K.

A blade or tongue E is fastened to C by means of a clip D and fits over the opening of the part that has been cut away. This tongue is made from_ thin sheet steel and carries at the end a contact-piece H which is set close to the mercury G contained at the bottom in the outer glass tube A.

If now C is connected to the water main by means of some rubber tubing, the water- pressure will vibrate the tongue E and the contact-piece H will be alternately dipped into the mercury and lifted out of it, thus closing and opening the primary circuit of the spark-coil.

After the water has passed the tongue E it accumulates over the mercury till it reaches the glass tube F by which it is drained away. The water passing over the mercury cools it and also the contact-piece H and keeps both in a clean state, which insures sharp interruptions.

The break shown in the general arrange- ment is mounted in a sloping position, so as to use as little mercury as possible.

To make the interrupter, procure first a glass tube 2 in. in diameter by 9 in. long. Have it cut to the right length in the store where you buy it, as it is very difficult to make a neat job of it and you may break the tube in the attempt. Next procure 2 soft rubber stoppers to fit the tube and see that these stoppers are a water-tight fit. Bore a hole in each stopper to admit the tubes C and F. Next take the tube C in hand. This is a hard rubber tube. 5^-in. bore by 6^ in. long. A portion 3 in. long must be cut away as shown in the detail drawing. The easiest way of doing this is to cut to the depth required 3 in. from one end with a fretsaw, and then to file the tube down till the distance from the center of the tube to the cut-away part is J^^ in. Next fit a cork stopper K, \^ in. in diameter and

��Y2 in. long into the end of the tube C that has been cut away, and cut off the pro- jecting part.

The tongue E is now cut from thin springy steel to the dimensions given in de- tail drawing. A small copper-strip H is finally soldered to E and bent so as to be at right angles to the mercur>^ level.

The clip D is made from thin sheet steei and fitted around the cut-away part of C.

The tongue E is next soldered to the inside of D so that the tongue is lying flat against the tube in the entire length of the cut-away part.

Tongue and clip are now given 2 coats of good shellac varnish, but the contact-piece H must be left free from varnish.

To assemble the interrupter put the 2

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The parts of the interrupter which is operated by means of a flow of water instead of magnets

tubes C and F in position. After having soldered a No. 12 gage copper wire to the top of the clip £, this wire is carried through B, as is also a second wire that makes contact with the mercMry. Next pour some mercury into the glass tube A and bend E so that H is about 1/32 in. above the mercury level.

The tube is then mounted on a board by means of 2 small clips.

The 2 wires from D and G are connected to two binding posts mounted on the board.

To regulate the number of vibrations per second, slip an adjustable pinchcock over the rubber tube from the water-main to tube C, and use this as a means of govern- ing the flow of water.

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