WATER SOFTENING, specifically the process of eliminating from water the calcium (lime) and magnesium compounds which com bine with soap, forming insoluble curds and prevent the formation of lather, thus making the water 'hard.' In general the term em braces all forms of removal from water of any substance, lime, magnesia, acid, silt or other material which renders the water unsuitable for industrial use. The process has usually three phases: (1) the removal of scale-forming sub stances; (2) the neutralization or removal of corroding substances• (3) the separation of suspended matters. The first two are chemical; the third, mechanical. Rain water contains only the soluble gases of the air, carbonic acid gas, oxygen, ammonia and sulphurous acid and such dust and dirt as it may have washed out of the air in its fall. The water falling at the last end of a long rainstorm is nearly pure. Such water mixes readily with soap to form a slippery lather and the water is said to he soft. If rain water runs down a clean, grassy slope to a stream, it is still nearly pure soft water. If it runs over limestone or ground containing particles of limestone, it dissolves a small amount, perhaps two grains per gallon (of 58.391 . grains) or one part of limestone to about 29,000 parts of water; but for practical is still called soft water. If, er, the rain water sinks into the ground to remain a long time in contact with lime stone, it dissolves greater amounts, frequently Al grains per gallon of water and sometimes more than 100 grains per gallon. Water is commonly said to be hard if it contains more dam five grains per gallon. Deep well waters are isearly always of this nature. In the arid plains of the western part of the United States where the soil contains large quantities of common salt (chloride of sodium) and the other salts of sodium and potassium which are all readily soluble in water, the well waters are usually heavily charged not only with the salts of cal cium and magnesium but also with the salts of sodium and potassium and such water is called alkali water. The water which is found near the coal fields frequently contains sulphuric acid to the amount of two or three grains per gallon.
Lakes contain the waters of many creeks and rivers and are usually soft water; but the cur rent is slow or absent altogether and the evapo ration from the broad surface has the effect of concentrating the volume of dissolved salts so that lake water contains rather more min eral matter than river water and is frequently on the border line between soft and hard. Lake Erie water, the softest of all the lakes, con tains about five grains per gallon of the salts of calcium and magnesium. The oceans are the final receptacles for the waters of the rivers and lakes and are subject to continuous evaporation, so that in the course of years the mineral matter has become concentrated and ocean water contains about 2,100 grains per gallon of mineral matter, made up of calcium carbonate, eight grains; calcium sulphate, 75 grains; magnesium sulphate. 99 grains; mag nesium chloride, 230 grains; potassium sulphate, 55 grains; and sodium chloride, 1,633 grains; the great amount of sodium chloride and the relative scarcity of calcium and magnesium compounds being due to reactions which have taken place in the water, precipitating the salts last mentioned. Great Salt Lake in Utah and
the Dead Sea in Palestine (q.v.) are small bodies of water, like oceans, without known outlets, and since the rivers feeding them are heavily charged with common salt, these lakes contain much more of it in proportion than the oceans. Ocean water contains about 3.5 per cent mineral matter, the Dead Sca 26 per cent and Great Salt Lake averages about 20 per cent.
When hard waters are evaporated the min eral matter is left in a solid mass, interesting examples being found in the stalactites and stal agmites in caves and in the deposit in the bot toms of tea kettles. The most serious damage produced by hard water in industrial opera tions is the scale deposited in steam boilers and the waste of soap in washing. Scale in boilers is a deposit of the mineral content of the water evaporated, due in large part to the fact that some of the dissolved salts are more soluble in cold water than in hot and as the temperature rises the overplus isprecipitated as a crust on the inside of the boiler plates. This condition prevents the easy passage of heat from the fire to the water and shortens the life of the boiler because of the temperature to which the steel must he raised in order to force the beat through the scale to the water. The average heat conductivity of boiler scale is one thirty-seventh of that of the iron of which the boiler is made when the scale is thin. If thick this figure is much too large. The amount of extra fuel required to evaporate water in a boiler which is coated with scale varies with the thickness and character of the scale and with the rate at which the boiler is worked. When the boiler is being driven to nearly its full capacity, the amount of additional fuel re quired by a one-quarter-inch layer of scale is frequently as much as 50 per cent; but if the boiler is being worked at only half its capacity the difference may not be more than 10 per cent. Nearly all tables of such data are based on measurements of the additional amount of fuel required in a scale-covered boiler to heat the water at the same rate as in a clean boiler worked at normal capacity. It is estimated that the railroads of the United States are spending at least $15,000,000 annually in additional fuel and boiler repairs due to the hard and muddy water used in some parts of the country. Us ing hard water in boilers is much more expen sive than softening it, since on the average 1,000 gallons of hard water will do 50 cents worth of damage in fuel and repairs, while 1,000gallons of hard water may almost always be softened for less than 3 cents. The value of the soap wasted by hard water is enormous, amounting to 1.7 pounds per 1,000 gallons of water for each grain of hardness, or 17 pounds per 1,000 gallons of water 10 grains hard per gallon, a value of at least 70 cents, when it would cost perhaps two cents per 1,000 gallons on the average to sufficiently soften such water.