It is evident that the whole subject of boiler feed waters and their treatment is one for the chemist rather than for the engineer. A brief outline of the difficulties that may be experienced from the use of poor feed water and a suggestion as to a method of overcoming certain of these difficulties is all that will be attempted here. Such a brief outline of the subject, however, will indicate the necessity for a chemical analysis of any water before a treatment is tried and the necessity of adapting the treatment in each case to the nature of the difficulties that may be experienced. Table 14 gives a list of impurities which may be found in boiler feed water, grouped according to their effect on boiler operation and giving the customary method used for overcoming difficulty to which they lead. Scale--Scale is formed on boiler heating surfaces by the depositing of impurities in the feed water in the form of a more or less hard adherent crust. Such deposits are due to the fact that water loses its soluble power at high temperatures or because the concentration becomes so high, due to evaporation, that the impurities crystallize and adhere to the boiler surfaces. The opportunity for formation of scale in a boiler will be apparent when it is realized that during a month's operation of a 100 horse-power boiler, 300 pounds of solid matter may be deposited from water containing only 7 grains per gallon, while some spring and well waters contain sufficient to cause a deposit of as high as 2000 pounds. The salts usually responsible for such incrustation are the carbonates and sulphates of lime and magnesia, and boiler feed treatment in general deals with the getting rid of these salts more or less completely. TABLE 15 SOLUBILITY OF MINERAL SALTS IN WATER (SPARKS) IN GRAINS PER U. S. GALLON (58,381 GRAINS), EXCEPT AS NOTED +------------------------------+------------+-------------+ |Temperature Degrees Fahrenheit| 60 Degrees | 212 Degrees | +------------------------------+------------+-------------+ |Calcium Carbonate | 2.5 | 1.5 | |Calcium Sulphate | 140.0 | 125.0 | |Magnesium Carbonate | 1.0 | 1.8 | |Magnesium Sulphate | 3.0 pounds | 12.0 pounds | |Sodium Chloride | 3.5 pounds | 4.0 pounds | |Sodium Sulphate | 1.1 pounds | 5.0 pounds | +------------------------------+------------+-------------+ CALCIUM SULPHATE AT TEMPERATURE ABOVE 212 DEGREES (CHRISTIE) +------------------------------+----+----+-------+----+---+ |Temperature degrees Fahrenheit|284 |329 |347-365| 464|482| |Corresponding gauge pressure | 38 | 87 |115-149| 469|561| |Grains per gallon |45.5|32.7| 15.7 |10.5|9.3| +------------------------------+----+----+-------+----+---+