Economy Of Soft Waters

Throughout the Mississippi Valley and in other parts of the United States where municipal water supplies are obtained from artesian wells drilled to the underlying St. Peter or Potsdam sandstone, the water is permanently, and in some localities, both temporarily and permanently hard. This is due to the fact that in those regions the geological formation of the upper strata is limestone, and in percolating through the limestone, the water, which originally was soft, dissolves from rock, carbonates or sulphates of lime or magnesia. The solvent capacity of water for carbonates and sulphates of lime is greater when the water is cold, therefore, deep well waters in limestone regions usually are saturated with lime or magnesia, and when heated in water tanks or boilers to a temperature greater than 140 degrees Fahr., the point of saturation is lowered and lime is precipitated or liberated and forms a hard scale or incrustation in waterbacks and boilers. The effect of boiler incrustation is to shorten the life of a boiler and decrease the efficiency of the apparatus while in service. It is accepted by good authority that:

Table XLII - Dimensions And Capacity Of Jewell Pressure Filters

1/16-inch lime scale means a loss of 13 per cent. of fuel. 1/8-inch lime scale means a loss of 22 per cent. of fuel. 1/4-inch lime scale means a loss of 38 per cent. of fuel. 3/8-inch lime scale means a loss of 50 per cent. of fuel. 1/2-inch lime scale means a loss of 60 per cent. of fuel. 3/4-inch lime scale means a loss of 91 per cent. of fuel.

These values are probably a little high, but making due allowance for inaccuracies the table still serves to show the enormous waste of coal due to boiler incrustation.

Incrustation of waterbacks and water heaters not only decreases their efficiency while in service, but is also a source of expense for repairs. In limestone regions waterbacks and heaters become choked with lime and require cleaning at certain intervals of time ranging from one to six months.

In the household, the increased consumption of soap to soften hard water is a further item of expense. The amount of commercial soap required for this purpose, with waters of different degrees of hardness, can be seen by the following table:

Table XLIII - Soap Required To Soften Water

Many industrial concerns, like breweries, paper mills and laundries require soft water, not only for boiler feed, but also for industrial purposes, and use some modification of the Clark-Porter water softening process.

The Clark process consists of adding lime water to temporarily hard water to remove the carbonates of lime or magnesia. The lime acts upon the bicarbonates in the hard water, releasing the extra carbonic acid gas required to form the bicarbonates, and precipitates the carbonates of lime which are insoluble.

The Porter process consists of adding soda ash to permanently hard water to remove the sulphates of lime and magnesia, and stirring up the treated water with paddles to mix it. When soda ash is added to permanently hard water, it reacts upon the sulphates of lime and magnesia, decomposes them and forms insoluble carbonates which are precipitated.

The reagents generally used in water softening are caustic lime (common quick lime) and soda ash. Other reagents can be used, but the above are generally selected on account of their cheapness and because they are readily obtainable in any market.