SCALE-MAKING AGENCIES.
Water, as has been mentioned, is the most universal solvent in nature; and what is known as hard water contains many foreign ingredients, but those that exercise such a pernicious influence upon locomotive boilers are lime and magnesia. The scale-making lime appears in two forms,—sulphate of lime, and carbonate of lime. The former is the more dangerous and troublesome scale-making agent; the latter is most frequently met with.
Ordinary well-water will be found to contain solid matter in solution varying from 10 to 100 grains to the gallon. Under 20 grains to the gallon of impurities may be considered fair water if the principal ingredient is carbonate of lime, but that amount of sulphate will make highly objectionable boiler water. Where the use of well-water is unavoidable on a road, quite a saving to boilers can be effected by ascertaining the quantity and character of the impurities received from each water-tank, and directing the engineers to avoid those that contain the worst scale formers.