It has been found that water of fourteen degrees of hardness lost two degrees when merely made boil; boiling for five minutes reduced the hardness to six degrees; and for a quarter of an hour, to little more than four degrees. The practical application of this knowledge needs scarcely to be pointed out. Whenever a soft water is required, boil for several minutes before using. In making tea, for instance, the economy and general superiority of soft water is well known. Those, however, who use Thames water, just made to boil, employ a water of upwards of eleven degrees of hardness: those who boil for five minutes, diminish the hardness of the water by nearly one-half; and by boiling for a quarter of an hour, it can be lessened to one-third. This circumstance is one of those that prove how great a substratum of truth there is at the bottom of most popular notions. How many a young gentleman, with a smattering of science just enough to inform him that water gets no hotter however long or violently it is boiled, has laughed at his grandmother’s antiquated notions, because she requested that the water might be made to boil thoroughly before the tea was made: the old lady could give no very satisfactory explanation of her prejudice, yet it was not the less a correct one. Before going further in this matter, it may be stated that there are some waters in which the lime is dissolved in the form of gypsum (sulphate of lime); in these, which fortunately are rare, the hardness is of a permanent character, and cannot be lessened by boiling. Tea made under such circumstances may be improved, either by the addition of a _very small_ quantity of carbonate of soda, or the tea should be kept soaking for half an hour, under such circumstances as will retain the heat. This latter is the plan followed in Greenwich Hospital, where they use a well water of nineteen degrees of permanent hardness. In washing, the use of hard water is, as is well known, extremely prejudicial. The explanation is exceedingly simple: every degree of hardness in a gallon of water destroys ten grains of soap; and by following out the calculation, it will be found that 100 gallons of unboiled Thames water waste exactly two pounds of soap before any approach to a lather can be made. Now what is the remedy for this evil? Simply to boil the water some time before use; one quarter of an hour’s boiling will reduce the waste of soap from two pounds to ten ounces; and half an hour’s boiling will still further lessen it to six ounces; but no amount of boiling will make Thames water equal to rain water, which is without hardness.