49 



ment with the necessary amount of lime. The relative cost of 

 softening by boiling and by lime is given by Collett"^ as 50 to 1. 



Class II. Includes those waters which have sufficient sodium 

 to unite with all the nitrates and chlorides and with part of the 

 sulphates present. These waters contain the sulphate of mag- 

 nesium and sometimes the sulphate of calcium, iron and alu- 

 minium. The waters of this class will form a scale more or less 

 hard, according to the proportion of sulphate present. Their 

 soap-consuming power may be high, and boiling will not re- 

 move all of the hardness. Boiling will remove the carbonate 

 hardness, but the sulphate hardness will remain. Lime will 

 remove the carbonates, but soda ash or caustic soda must be 

 used to change the sulphates to sulphates of sodium. 



Class III. Includes those waters in which the sodium is not 

 present in sufficient quantity to unite with all the nitrates and 

 chlorides present. These waters will therefore contain mag- 

 nesium chloride. The hardness may be due to chlorides, sul- 

 phates and carbonates of magnesium, calcium, etc. These waters 

 will be corrosive, and will form a hard scale and pit when used 

 in boilers. They will also consume a considerable quantity of 

 soap, and the hardness will not all be removed by boiling. As in 

 Class II lime will remove the carbonates, but soda ash or 

 caustic soda must be used for the mineral acid hardness. 



It is noted that the waters of the second class are most com- 

 mon, there being 64 waters in this class. The first class is next 

 in order with 32 waters, and the third class numbers 10. 



Most of these waters will yield to treatment, the exception 

 being those containing a large residue. These may be softened, 

 but because of the necessary addition of sodium salts in the 

 softening process the foaming constituents will be increased so 

 that they will be unsatisfactory for boiler uses. With the ex- 

 ception of the waters just mentioned, it is possible to so treat 

 the Illinois waters that corrosion will be prevented and the 

 scaling ingredients reduced to less than 85 parts per million (5 

 grains per gallon). 



* Water Softening and Purification, London, 1908, p. 3. 



