Some kinds of soft coal form "clinkers," and these catch in the grate. In burning fuel that makes clinkers, shake the ashes from the fire several times a day. Remove all accumulations in the fire box daily. Clinkers are made from substances which melt and recombine, forming a different material which is quite hard and does not burn. Constant attention to the fire prevents clinkers from forming in large masses.
CHAPTER XI
Gas, Electric and Kerosene Heaters
77. Kinds of Gas Heaters. There are several types of gas heaters—those using an illuminating flame and reflector, those fitted with a Bunsen burner and an asbestos back, and those heating water in a device like a radiator. The last two burn with a blue flame. All gas stoves ought to be fitted with a flue for discharging the products of combustion.
Fig. 39. Gas heater showing air mixer.
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).