The mineral matter is the least objectionable as it is also the most common, since all water is forced to partake, more or less, of the nature of the rocks and soil over which it passes. Good waters contain from twenty to one hundred grains per gallon of mineral salts; that is, of various chemical substances which are able to be dissolved by water. If the amount is much in excess of one hundred parts, the water is noticeably "hard," and this may increase to a point where the water cannot be used. For example, the writer once superintended the locating and drilling of a well which passed through a bed of sodium sulphate or gypsum, just before reaching the water, so that as the latter rose in the well it dissolved and carried with itself a large amount of this salt, so much that the water was useless. Water containing more than one hundred grains per gallon of such salts as magnesium sulphate or sodium phosphate is a mineral water rather than a good drinking water, and while an occasional glass may do no harm or may even have desirable medicinal effects, such a water is not fit for constant drinking. It is worth noting that many attempts have been made to show the relative effect of various hard waters on the health. A French commissioner reported that apparently people in hard-water districts had a better physique than in soft-water districts. A Vienna commissioner also reported in favor of a moderately hard water for the same reason. It is to-day believed by many that children ought to have lime in water; that is, ought to drink hard water to prevent or ward off "rickets" or softening of the bones. An English commissioner, on the other hand, has concluded that, other things being equal, the rate of mortality is practically uninfluenced by the softness or hardness of the water-supply. This same commissioner has also shown that in the British Isles the tallest and most stalwart men were found in Cumberland and in the Scotch Highlands, where the water used is almost invariably very soft (Thresh's "Water-supplies"). It has been asserted that certain diseases, not necessarily causing death, are caused by hard water, as calculus, cancer, goiter, and cretinism; but, as already pointed out in Chapter II, no satisfactory proof has ever been established. One must conclude that within reasonable limits there is little to choose between a hard and soft water for drinking purposes, although a change from a soft water to a hard, or _vice versa_, usually produces temporary derangements. _Loss of soap._ For washing purposes the value of a soft water is more marked. When a hard water is used, a certain amount of soap is required to neutralize the hardness before the soap is effective, and this takes place at the rate of about 2 ounces of soap to 100 gallons of water for each part of calcium carbonate per gallon, or about 3 ounces of soap to 10,000 gallons for each part per million increase in hardness.