LIME, SCALE, AND MUD.
In calcareous regions, where the water-supply for locomotives is drawn from wells, the most common cause for bad-steaming engines is leaky heating-surfaces, or water-surfaces incrusted with lime deposits. When he sees water pouring from flues and stay-bolts, an engineer has no difficulty in divining the reason why his engine steams poorly; nor need he be far-seeing to perceive a remedy in the boiler-maker’s calking-tools skillfully applied. The case of incrustation is, however, more difficult to comprehend in all its bearings. When water containing lime-salts touches the hot flues or fire-box, evaporation takes place; and the solid substance previously in solution is left behind, and adheres to the heating-surfaces, gradually forming a refractory scale which is an indifferent conductor of heat. As this scale becomes thick, it stands up, like a non-conducting barrier, between the water and the hot sheets; and it takes a much greater expenditure of heat to evaporate the water inside, just as a kettle coated with scale is much harder to boil than a clean one. When a boiler gets badly fouled with scale and mud, these impurities exercise a pernicious effect upon the steaming qualities of a locomotive.