The proportions of its elements are 60.4 per cent. of chlorine and 39.6 per cent. of sodium.
In salt made of sea water the salts of magnesia with a little sulphate of lime are the principal impurities.
The above mentioned chemical substances can be classified into two distinct classes, i.e., incrusting and non-incrusting.
Of the incrusting salts, carbonate of magnesia is the most objectionable, and any feed water that contains a dozen grains per gallon of magnesia can be expected to have a most injurious effect on the boiler, causing corrosion and pitting. Carbonate of lime, while not as bad as the magnesia carbonate, yet has a very destructive action on a boiler and 20 grains per gallon of this is considered bad water. All silicates, oxides of iron, and aluminium, and sulphate of lime are also incrusting. The non-incrusting substances are three, viz., chloride of sodium (common salt), and sulphate and carbonate of soda.
Note.
In view of the increasing importance laid upon a knowledge of the chemical formation of feed water, these chapters of Chemical Terms and Analysis of Feed Waters are given to indicate the direction in which the advanced engineer must push his inquiries. There are more millions of treasure to be made by properly “treating” the water which enters the steam generators of the world than can be extracted from its gold mines.
An important “point” is to make sure, before adopting any permanent system for purifying the waters of a steam plant, that it is always the same in its ingredients, i.e., that the impurities contained in the water are the same at all times.