USES OF WATER.

A limited quantity of water actually enters into chemical reactions in industry in comparison with the vast amount that is unchanged during use. Water consumed by animals and man to sustain life and maintain health also represents a small part of the total. The bulk of water that enters into the national economic picture functions on the basis of its physical properties. Much of this may contain some dissolved and suspended matter without being objectionable.

Drinking water must be very low in dissolved matter largely because of taste, but also physiological action is an important factor. Least objectionable are such materials as sodium chloride and sodium bicarbonate, while iron, calcium, and magnesium salts are quite undesirable. Organic matter is barred, particularly if derived from sewage or plant wastes.

With the development of high-pressure boilers, the water fed to such equipment must be of a very high degree of purity. Concentration is very rapid and all materials that will cause foaming, corrosion, or scale must be absent. Even small amounts of silicates, which would have been neglected in the past , are now removed.

Alkaline compounds, especially salt and soda. Are objectionable in water employed in irrigation since they remain in the soil in evaporation, and in dry climates are not sufficiently removed by rainfall.

In the chemical process industries there are great variations in the types of water that may be employed. Iron is particularly objectionable in many processes. In the textile and laundry industries where detergents are employed, soap is incompatible with calcium and magnesium salts, but synthetic detergents do not form the same type of sticky precipitates. Naturally, a high degree of purity is required in food, pharmaceutical, and fine chemical industries.

Water employed primarily as a coolant does not have to de exceptionally free from dissolved material, and even seawater is used if a certain amount of corrosion can be tolerated or if it is economical to employ highly resistant materials of construction.