170 



Temporary Hardness. Temporary hardness, so called from 

 the fact that it may be removed by boiling, is due to the presence 

 of the bicarbonate of lime in the water. 



While boiling is effective in reducing the temporary hardness, 

 its application will naturally be limited to families where the 

 amount of water required is small. Where softening has to be 

 conducted on a large scale, chemical treatment is the only satis- 

 factory method. 



To the water to be softened, lime water or milk of lime, made 

 by dissolving commercial lime in water, is added. The lime re- 

 acts with the soluble bicarbonate of lime (to which the tempo- 

 rary hardness is due), forming an insoluble carbonate which is 

 precipitated. About .8 pound of lime to 1000 gallons or I pound 

 to 165 cubic feet is required when the water to be treated contains 

 (as determined by chemical analysis) 10 grains of bicarbonate to 

 the gallon. Proportional amounts will be required for waters 

 with greater or smaller quantities of the bicarbonate. 



Permanent Hardness. Permanent hardness, or that which 

 is not removed by boiling, is due mainly to the presence of the 

 sulphates. of lime or magnesia. It may be neutralized by the 

 addition of soda-ash, or impure carbonate of soda. About I 

 pound of soda-ash of 78 per cent strength or if pounds of 56 

 per cent strength are required to each 1000 gallons of water or 

 each 135 cubic feet. 



The chemical is usually added, after being dissolved and fil- 

 tered, by mechanical appliances to the water of tanks or settling 

 basins. By its action, the soluble sulphate of lime is converted 

 into the insoluble carbonate and precipitated, leaving sodium sul- 

 phate in solution. 



Alkalinity. Certain well waters of the southern portion of 

 the Atlantic Coastal Plain and many of the well and surface 

 waters of the arid and semi-arid regions of the West contain 

 considerable quantities of alkali, especially sodium carbonate, 

 in solution. This gives to light colored vegetables cooked in 

 such waters a yellowish color that is very objectionable, and, 



