in each gallon. Very little chalk (only two grains in every gallon) can be dissolved by pure water. The large quantity found in river and spring water is dissolved by means of a gas, called carbonic acid gas, which is always present. When the water is heated this gas is driven off in small bubbles, which may be seen just before the water reaches the boiling point; the chalk is then thrown down in a solid form, rendering the water slightly cloudy or turbid, and afterwards it settles down on the sides and bottoms of boilers or kettles forming the rock or fur which is always found in old boilers.
When green vegetables are boiled in hard water, the chalk causes them to be of a dull colour; and when clothes are boiled in hard water, as is sometimes done in washing, the rock or fur settles on them, causing them to be of a bad colour, the dirt being fixed in the clothes.
When hard water is used for cooking or washing it is best to boil it for a few minutes before using it, as then the fur is thrown down on the sides of the boiler, and not on the food or clothes. Hard water is not good for making tea, as the strength of the tea-leaves is very slowly extracted.
The bad effects of hard water in cooking may be partly remedied by using a small quantity of carbonate of soda, or even common washing soda, this softens the water, but if much be added it gives a soapy, unpleasant taste; as much as would cover a sixpenny-piece may be added to a large saucepan of greens, and about a quarter as much to a large teapot of tea.
79. Spring or well water differs very much in purity, which is collected in shallow wells should
CH. XII.] WATER SUPPLY—QUALITIES, &c. 75
never be used in places that are thickly populated or highly manured, for the water is rendered impure by the decaying animal and vegetable substances in the soil, and becomes very unwholesome.
When shallow wells are situated near cesspools or drains, the water becomes quite poisonous, and gives rise to cholera, fevers, and other fatal diseases. The water of wells situated in large cities, or near grave-yards, is always to be avoided.
80. The water from deep wells is generally free from any decaying vegetable matter or drainage, and is wholesome as a beverage, but it most frequently is excessively hard from containing a large amount of chalk dissolved in it.
81. Rain water is very pure if collected in country districts where there is but little smoke, but in towns it is always blackened by soot. It is very soft, being perfectly free from mineral substances, and if collected in proper tanks free from leaves of trees and other decaying substances is very well fitted for cooking, drinking and washing.