treatment in general
deals with the getting rid of these salts more or less completely.

TABLE 15

SOLUBILITY OF MINERAL SALTS IN WATER (SPARKS)
IN GRAINS PER U. S. GALLON (58,381 GRAINS), EXCEPT AS NOTED

+------------------------------+------------+-------------+
|Temperature Degrees Fahrenheit| 60 Degrees | 212 Degrees |
+------------------------------+------------+-------------+
|Calcium Carbonate | 2.5 | 1.5 |
|Calcium Sulphate | 140.0 | 125.0 |
|Magnesium Carbonate | 1.0 | 1.8 |
|Magnesium Sulphate | 3.0 pounds | 12.0 pounds |
|Sodium Chloride | 3.5 pounds | 4.0 pounds |
|Sodium Sulphate | 1.1 pounds | 5.0 pounds |
+------------------------------+------------+-------------+

CALCIUM SULPHATE AT TEMPERATURE ABOVE
212 DEGREES (CHRISTIE)

+------------------------------+----+----+-------+----+---+
|Temperature degrees Fahrenheit|284 |329 |347-365| 464|482|
|Corresponding gauge pressure | 38 | 87 |115-149| 469|561|
|Grains per gallon |45.5|32.7| 15.7 |10.5|9.3|
+------------------------------+----+----+-------+----+---+

Table 15 gives the solubility of these mineral salts in water at various
temperatures in grains per U. S. gallon (58,381 grains). It will be seen
from this table that the carbonates of lime and magnesium are not
soluble above 212 degrees, and calcium sulphate while somewhat insoluble
above 212 degrees becomes more greatly so as the temperature increases.

Scale is also formed by the settling of mud and sediment carried in
suspension in water. This may bake or be cemented to a hard scale when
mixed with other scale-forming ingredients.

Corrosion--Corrosion, or a chemical action leading to the actual
destruction of the boiler metal, is due to the solvent or oxidizing
properties of the feed water. It results from the presence of acid,
either free or developed[15] in the feed, the admixture of air with the
feed water, or as a result of a galvanic action. In boilers it takes
several forms:

1st. Pitting, which consists of isolated spots of active corrosion which
does not attack the boiler as a whole.

2nd. General corrosion, produced by naturally acid waters and where the
amount is so even and continuous that no accurate estimate of the metal
eaten away may be made.

3rd. Grooving, which, while large