Range Of Solvency

Water is an almost universal solvent. Its range is greater than any other known liquid. It dissolves to a greater or less extent all minerals, and many metals with which it is brought in contact. As a rule, the solvent power of water increases with its temperature, but for common salts the solvent power is nearly constant at all temperatures. Lime salts are more soluble in cold than in hot waters, and it is due to this latter fact that incrustation of water backs takes place in regions when the water supply is hard. In percolating through the earth the water dissolves carbonates or sulphates of lime or magnesia from lime rocks, until the water reaches the point of saturation; then, when subjected to heat in a water back or heater, the point of saturation of the water is lowered, thus liberating some of the lime or magnesia which settles upon and becomes baked to the walls of the water back or heater.

The proportion of mineral that can be dissolved by a given quantity of water depends upon the nature of the mineral, the kind of water and its temperature. The relation between soluble minerals and water is absolute. That is, at a given temperature a certain quantity of water will dissolve a definite quantity of mineral salts; if a quantity greater than this be added to the water, the amount in excess will settle to the bottom of the vessel. The water is then saturated, and the mixture is a saturated solution. By increasing or decreasing the temperature of the water, as the nature of the mineral requires, a greater quantity can be dissolved.

The greatest quantity of various substances in common use that can be dissolved by one imperial gallon of water can be found in the following table. The figures do not indicate the weight of chemical contained in a gallon of saturated solution.

Table XV - Solubility Of Water (Collett)

+Insoluble at about 290 degrees Fahrenheit.

*Decomposes at boiler temperatures in presence of alkaline earths or iron.

# Insoluble at 302 degrees Fahrenheit, equal to 70 pounds steam pressure.