Mineral waters are those which have extracted from the soil and rocks through which they have passed sufficient quantities of mineral matters to give them a distinct character. These dissolved matters are of the most varied character. They consist largely of the salts of the ordinary bases, namely, soda, potash, lime, magnesia, and iron and more rarely lithia and radio-activity. The rarer elements are sometimes found in these waters, but only in minute quantities. Occasionally poisonous principles, such as arsenic, alum and copper, are found dissolved in waters of this character. In general, it may be said that the use of mineral waters as a regular beverage is not to be commended. These waters are useful for special purposes, which will be described further on.