Hardness: 100 cubic centimeters of the treated water is used for this test, one cubic centimeter of the soap solution corresponding to one degree of hardness. The soap solution is added a very little at a time and the whole violently shaken. Enough of the solution must be added to make a permanent lather or foam, that is, the soap bubbles must not disappear after the shaking is stopped. Excess of lime as determined by nitrate of silver: If there is an excess of lime used in the treatment, a sample will become a dark brown by the addition of a small quantity of silver nitrate, otherwise a milky white solution will be formed. Combined Heat and Chemical Treatment: Heat is used in many systems of feed treatment apparatus as an adjunct to the chemical process. Heat alone will remove temporary hardness by the precipitation of carbonates of lime and magnesia and, when used in connection with the chemical process, leaves only the permanent hardness or the sulphates of lime to be taken care of by chemical treatment. TABLE 16 REAGENTS REQUIRED IN LIME AND SODA PROCESS FOR TREATING 1000 U. S. GALLONS OF WATER PER GRAIN PER GALLON OF CONTAINED IMPURITIES[16] +-----------------------+-----------+-----------+ | | Lime[17] | Soda[18] | | | Pounds | Pounds | +-----------------------+-----------+-----------+ | Calcium Carbonate | 0.098 | ... | | Calcium Sulphate | ... | 0.124 | | Calcium Chloride | ... | 0.151 | | Calcium Nitrate | ... | 0.104 | | Magnesium Carbonate | 0.234 | ... | | Magnesium Sulphate | 0.079 | 0.141 | | Magnesium Chloride | 0.103 | 0.177 | | Magnesium Nitrate | 0.067 | 0.115 | | Ferrous Carbonate | 0.169 | ... | | Ferrous Sulphate | 0.070 | 0.110 | | Ferric Sulphate | 0.074 | 0.126 | | Aluminum Sulphate | 0.087 | 0.147 | | Free Sulphuric Acid | 0.100 | 0.171 | | Sodium Carbonate | 0.093 | ... | | Free Carbon Dioxide | 0.223 | ... | | Hydrogen Sulphite | 0.288 | ... | +-----------------------+-----------+-----------+ The chemicals used in the ordinary lime and soda process of feed water treatment are common lime and soda. The efficiency of such apparatus will depend wholly upon the amount and character of the impurities in the water to be treated. Table 16 gives the amount of lime and soda required per 1000 gallons for each grain per gallon of the various impurities found in the water. This table is based on lime containing 90 per cent calcium oxide and soda containing 58 per cent sodium oxide, which correspond to the commercial quality ordinarily purchasable. From this table and the cost of the lime and soda, the cost of treating any water per 1000 gallons may be readily computed.