This section is from the book "The Boy Mechanic Vol. 2 1000 Things for Boys to Do", by Popular Mechanics Co.. Also available from Amazon: The Boy Mechanic, Vol2: 1000 Things for Boys to Do.
A very simple and inexpensive electric gas-lighting device is shown in the accompanying illustration. The gas is ignited by means of an electric spark which is produced between the two parts A and B of an electric circuit. This circuit is composed of a source of electrical energy, such as a number of dry cells, a kick coil, the connecting leads, and a special operating switch for opening and closing the circuit to produce the spark. The circuit is normally open, but as the lever controlling the gas valve is moved from one position to the other, by pulling the chains, the lever C is caused to move through a certain arc. Now, as this lever C moves, its upper end passes the projecting point B, which is attached to the upper portion of the burner, and the electric circuit will be completed and broken. Just as the point A leaves contact with the point B an arc will be produced. This arc is greatly intensified by the kick coil, which acts as a sort of reservoir in which energy is stored while the circuit is closed, and upon opening the circuit this stored energy is given out by the kick coil and increases the size of the arc.
The points A and B should both be made of platinum, as other metals will not withstand the extremely high temperature of the arc. Pieces of platinum that will serve very nicely for the purpose may be obtained from an old incandescent lamp. The piece B is mounted on a brass collar, D, by means of a small screw, E. The brass collar D is held in place by the screw F, which draws the two ends together. This collar must be insulated from the stem or fixture by some thin sheets of mica. The upper end of the piece of platinum B should be just high enough to come within the lower edge of the gas flame.
Now mount an arm, C, on the valve stem so that it stands in a vertical position when the lever to which the chains are attached is in a horizontal position. Bend this arm into the form shown in the figure and cut its upper end off so that it is about 1/2in. below the outwardly projecting end of the piece of platinum B. Drill a small hole in the upper end of C, and insert a piece of platinum and run some solder around it.
Then the complete burner and valve are mounted on the gas fixture, and from the collar D an insulated wire is run to the point where the battery and kick coil are to be located. The gas fixture itself is to form one side of the electric circuit, and one terminal of the battery should be connected to the gas pipe as shown in the figure.
A kick coil may be made as follows: Procure a small quantity of rather small soft-iron wire and cut a sufficient number of 8-in. lengths to make a bundle about 7/8 in. in diameter. From some good writing paper make a tube, 8 in. long and 7/8 in. in outside diameter. Use at least six layers of paper and glue the various layers together in forming this paper tube. After the tube has dried thoroughly, fill it with the pieces of iron wire until it is perfectly hard. Cut from some 1/2-in. hard wood, two pieces, 3 in. square, and drill a 7/8-in. hole in the center of each of these to a depth of % in. Now glue these pieces to the completed core and the winding can begin as soon as the glue is dry. Wind on this spool six layers of double cotton-covered No. 18 gauge wire, insulating the various layers from each other with several thicknesses of good writing paper. This coil is then mounted on a wooden base and suitable terminals provided.
At least four dry cells will be required to give satisfactory results. Bear in mind that the gas must be escaping from the burner when the arc is formed. The adjustment of the arm A, as given above, may result in the gas valve being closed when the arc is formed, and the device will then fail to operate. If this is the case, the arm C should be loosened and moved back so that the circuit is broken at a later time while the valve is being moved from the "off" to "on" position. The circuit should be closed for some little time before it is opened so that some energy may be stored in the kick coil. If the wire A is made long enough to project a short distance above B, it will result in the circuit being closed for a longer time than it would if they just touched.