Popular Science Monthly 



479 



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 



t:-:£::::::::] ^ '^D 



c 



fef 



-^ -r 



33' 



(Q=S 



H" SOLDERED 

 / TO E' 



1=3): 



0_ -ll^ 



SHARP ED&t 



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. 



