carbonate of lime is dissolved only in water that contains carbonic acid gas, and the gas is driven off as soon as the water boils, and long before it has boiled away. It is upon this last reason that the softening of water by boiling depends. The harshness of water is also caused by sulphates. In the latter case boiling does not soften the water.
Organic impurities, by which is meant the animal and vegetable matter often present in water, are highly dangerous. Sewage contamination may exist in palatable sparkling water. This danger is increasing owing to the more and more prevailing custom of diluting sewage with water. The dangers and wastefulness of this system of drainage, especially when applied in country districts near the sources of our great water supplies, are clearly shown in the writings of those who have recently devoted considerable attention to this all-important subject.
Cisterns in which water is stored should be carefully cleansed at frequent intervals. Water brought on to premises in a pure condition may be contaminated by neglecting this precaution. Cisterns should also be provided with close-fitting lids; this prevents small animals and much dust from falling into the water.
To Purify Water.—Water that is unfit to drink is not made in any way less harmful by the addition of spirits, wine, or any flavouring matter. It may be rendered harmless by boiling, which is the only practicable household means of purifying water. Most of the decoctions and infusions are useful in this respect, because the water of which they are made must be boiled, the flavouring matter afterwards being added to conceal the insipidity. Boiled water can be aerated by pouring it from one jug to another, if only a small quantity has to be dealt with.
Filters should not be resorted to instead of boiling as a means of purifying water. Many simple forms of filters may be usefully employed as a mechanical means of separating suspended matter, but few, if any, remove or destroy impurities in perfect solution. Spongy iron, carbon and sand are valuable filtering agents, but one of the best mediums is porcelain, the only objection to filters made of this substance being the slow passage of the water through them.
Tea.—The most popular non-alcoholic beverage in this country is tea, now considered almost a necessary of life. Previous to the middle of the seventeenth century it was not used in England. Pepys says in his Diary: "September 25th, 1661.—I sent for a cup of tea (a China drink), of which I had never drunk before." Four years later it was so rare a commodity in England that the English East India Company bought 2 lbs. 2 ozs. of it as a present for his Majesty. In 1666 it was sold in London for 60 shillings a pound. From that date the consumption has gone on increasing from 5,000 lbs. to 215,000,000 lbs., an annual consumption of about 6 lbs. per head of the population of Great Britain.