The spark which occurs at the contact breaker of a Ruhmkorff coil is held in check by the condenser; were no condenser used, it would possess considerable powers of combustion. Using a large primary coil and a few cells of open circuit battery, this spark is made to pass across the path of a gas jet, which it instantly ignites. The contact breaker consists of a platinum point, fixed on the gas tip, and a German silver spring, carried on a lever, which latter is pulled across the tip so as to make and break the circuit at the burner orifice. Some burners are provided with a ratchet arrangement, by which pulling the lever once turns on and lights the gas, pulling again turns it off; others require the gas to be turned on first.
Reference to Fig. 56 will show the connections to two burners _P P_ and an automatic burner _A_, to be described later. The coil _C_ is a core of soft iron, about ¾ inch diameter and eight to ten inches long, wound with from two to four pounds of magnet wire, Nos. 12 or 14 B & S. One side of the battery goes to ground or to the gas pipe, thus forming the return circuit. The wiring on the fixtures is done with No. 20 to 24 B & S gas fixture wire, insulated with four windings of silk or cotton. This is fastened to the lacquered brass work by means of thick shellac varnish, it being tied on first with thread, which can readily be removed when shellac is dry and hard. The wire is held on the insulated collar of the burner by a small nut and screw, and great care must be taken to ensure no grounding. The setting up of a gas-lighting outfit is extremely simple, but it often fails for want of care. There must be the best possible insulation between wire and metal work.
There are several forms of these burners, but the principle of all is the same. A gas burner protrudes from the top of a brass case which encloses the actuating mechanism. This mechanism consists of two electromagnets, the armature of one opening a valve and allowing the gas to flow, at the same time vibrating a platinum-tipped rod, which produces a series of sparks at the burner tip. These sparks ignite the gas, and a second magnet is provided to shut off the flow of gas, thus extinguishing the light. Some devices use one electromagnet for both lighting or extinguishing, but the majority are with double magnets. The circuit is worked from a push button situated at any desired location, and having a white and black button, one for lighting and the other for extinguishing. The principal automatic burners are the Holtzer, the Boston, and the Bartholdi, between which there lies little choice, so admirably are they constructed.