=78. Bunsen Burner and Asbestos-Back Heater.= The burner is a long pipe punctured with holes extending across the stove. There is an opening for mixing of air with the gas at the point where this pipe enters the stove, and a valve to regulate the flow of gas (Fig. 39). =79. Lighting Gas Stoves.= To light the stove, open the valve, count three, and apply a lighted match to the burner. Counting three gives time for the pipe to fill with gas, so that the fire will not flash back and burn in the air mixer. =80. Care of Gas Stoves.= The only care that this stove needs is to keep it polished so that it will not rust. Keep the burner clean of dust and soot. Be sure that the valve is entirely closed when the gas is turned off, and that the pipes fit tight at all connections so that gas cannot leak into the room. [Illustration: FIG. 40. Reflector gas heater.] =81. Illuminating Flame and Bright Metal Reflector Heaters.= These heaters are used with manufactured gas. They burn with an illuminating flame since there is no device for mixing air with the gas as it enters the stove. The bright metal reflector not only makes an attractive stove, but reflects the heat out into the room. Some stoves are made with tips of aluminum or other non-corrosive metal over the openings in the burner (Fig. 40). Gas logs are a type of gas heaters used in fireplaces (Fig. 41). =82. Gas Radiator Heaters.= Gas radiators (Fig. 42) are another type of gas heater. The radiator is a coil of pipe. The heating unit is below the coil and works like any other Bunsen burner. A small amount of water is kept in the pipes. There is a device attached to the radiator to automatically adjust the height of the gas fire (_A_, Fig. 42). [Illustration: FIG. 41. Gas logs.] =83. Management of Gas Radiator.= Put enough water in the radiator or coil of pipe to fill it to the depth of one inch. Keep this amount of water in it at all times. Light a match, turn on the valve which lets gas flow into the burner, wait for it to fill with gas, and touch the match to the burner. Most of these heaters are fitted with thermostats. [Illustration: FIG. 42. Gas radiators.] In about thirty minutes after lighting the gas, the water will have formed enough steam inside the radiator to automatically turn the valve lowering the gas flame. If the steam pressure falls low, the thermostat will permit more gas to flow into the radiator by automatically opening the valve. There is a safety valve attached to the side of the radiator which opens if the automatic device fails to close off the gas before the steam pressure inside becomes too great.