~3.~ Water is also very necessary for other purposes. It softens our food so that we can chew and swallow it, and helps to carry it around in the body after it has been digested, in a way about which we shall learn in future lessons. ~4.~ Still another use for water is to dissolve and wash out of our bodies, through the sweat of the skin, and in other ways, the waste and worn-out particles which are no longer of any use. ~5. Impure Water.~--Most waters have more or less substances dissolved in them. Water which has much lime in it is called hard water. Such water is not so good to drink, or for use in cooking, as soft water. That water is best which holds no substances in solution. Well-water sometimes contains substances which soak into wells from vaults or cesspools. Slops which are poured upon the ground soak down out of sight; but the foul substances which they contain are not destroyed. They remain in the soil, and when the rains come, they are washed down into the well if it is near by. You can see some of the things found in bad water in the illustration given on opposite page. ~6.~ It is best not to drink iced water when the body is heated, or during meals. If it is necessary to drink very cold water, the bad effects may be avoided by sipping it very slowly. ~7. Tea and Coffee.~--Many people drink tea or coffee at their meals, and some persons think that these drinks are useful foods; but they really have little or no value as foods. Both tea and coffee contain a poison which, when separated in a pure form, is so deadly that a very small quantity is enough to kill a cat or a dog. This poison often does much harm to those who drink tea or coffee very strong for any great length of time. [Illustration: A DROP OF IMPURE WATER MAGNIFIED.] ~8. Alcohol~ (al'-co-hol).--All of you know something about alcohol. Perhaps you have seen it burn in a lamp. It will burn without a lamp, if we light it. It is so clear and colorless that it looks like water. The Indians call it "fire-water." Alcohol differs very much from foods. It is not produced from plants, as fruits and grains are; neither is it supplied by Nature ready for our use, as are air and water. ~9. Fermentation.~--When a baker makes bread he puts some yeast in the dough to make it "rise," so the bread will be light. The yeast destroys some of the sugar and starch in the flour and changes it into alcohol and a gas. The gas bubbles up through the dough, and this is what makes the bread light. This is called _fermentation_ (fer-men-ta'-tion). The little alcohol which is formed in the bread does no harm, because it is all driven off by the heat when the bread is baked. [Illustration: FERMENTATION.]