WATER SOLVENT ACTION OF WATER, ETC. 53 



be obtained with the soap and it is useless as a cleansing 

 agent. Hardness in water is consequently easily determined 

 by adding a standard soap solution to the water, which 

 will produce a greasy precipitate with the calcium and 

 magnesium salts in the water. Not till these salts are 

 all precipitated can a permanent lather be formed on the 

 surface of the water. The quantity of the soap solution 

 needed to produce the lather will, therefore, measure the 

 hardness of the water. 



Hardness may be classified as temporary hardness and 

 permanent hardness. Temporary hardness is usually caused 

 by the presence of dissolved bicarbonates of calcium and 

 magnesium. Permanent hardness is usually due to the 

 chlorides and sulphates of these elements. Calcium and 

 magnesium carbonates are insoluble, but if carbon dioxide 

 is present in the water, they dissolve to some extent, forming 

 the bicarbonates. Water having much hardness is objec- 

 tionable for drinking purposes. For bathing and laundry 

 purposes, it is expensive on account of the large amount 

 of soap incident to its use. 



Table III shows the relative efficiency of a number 

 of soaps for the purpose of softening water as given by 

 Whipple : 



According to Alexander Smith, with water containing 

 35 grains of hardness per gallon (60 parts per 100,000), 

 6 pounds of soap are wasted per 100 gallons of water before 

 the part of the soap that is to do the work of cleansing 

 begins to dissolve. 



When we consider that for each one part per million 

 of hardness it requires ten dollars' worth of soap to soften 

 one million gallons of water, it emphasizes the expense 

 in the use of hard water as a detergent. 



Temporary hardness may be removed : 



(1) By heating the water to boiling, so as to expel 

 carbon dioxide, in this way converting the soluble bicar- 

 bonate into an insoluble carbonate; 



