2. Is air necessary to combustion? Lower a candle or a burning splinter of wood into a bottle of air and cover as closely as pos- sible. Does it continue to burn ? 3. What is formed when fuel burns ? a. Hold a cold glass tumbler for a moment over a burning candle. Observe whether moisture forms on the inside of the glass. b. Burn a candle or a piece of wood in a covered bottle till flame is extinguished. COMBUSTION AND FUELS 99 Remove the candle or wood quickly and pour in a little lime water, and shake it around. Does it become milky? Try lime water in a clean bottle of air. Carbon dioxide is the gas which turns lime water milky. c. It is commonly said that food acts as fuel in the body. See if the "products of com- bustion", water and carbon dioxide, can be detected in the air breathed out. Test as follows : (1) Breathe on a cold pane of glass. Does moisture collect ? (2) Breathe through a glass tube or a lemonade straw into lime water. Do we breathe out carbon dioxide ? COMBUSTION AND FUELS When the word combustion is used, it ordinarily means burning, that is, the union of a substance with the oxygen of the air with such rapidity that both heat and light are produced. But in order to have this combustion take place, it is necessary to have something more than a com- bustible substance and oxygen. Wood is a combustible substance, but it does not burn unless it is sufficiently heated to " take fire." Not all materials have to be heated to the same degree to make them burn, and the point to which each must be heated is called the kindling tempera- ture of the substance. Phosphorus has a low kindling temperature and can easily be set on fire by the heat of friction ; that is why it is used on the heads of matches. Most combustible substances contain both carbon and hydrogen as well as a little oxygen. When they are burned 100 FOOD STUDY in the air the carbon unites with the oxygen to make carbon dioxide, and the hydrogen with oxygen to form water, oxygen from the air being used in the process. The com- mon fuels are inexpensive substances which are largely composed of these three elements. Foods, too, contain the same elements in large amounts. When food is burned in the body the process is a much slower one than ordinary burning and no light at all is produced, but the heat maintains the body temperature. Some fuels, like some foods, have nitrogen in them, but this does not help in the production of heat. The elements in fuels and foods are put together so differently, however, that they are entirely unlike in their nature, and the body could not burn coal or wood instead of food.

AI-modernized reading of the original text

2. Is air necessary to combustion? Lower a candle or a burning splinter of wood into a bottle of air and cover as closely as possible. Does it continue to burn ? 3. What is formed when fuel burns ? a. Hold a cold glass tumbler for a moment over a burning candle. Observe whether moisture forms on the inside of the glass. b. Burn a candle or a piece of wood in a covered bottle till flame is extinguished. Remove the candle or wood quickly and pour in a little lime water, and shake it around. Does it become milky? Try lime water in a clean bottle of air. Carbon dioxide is the gas which turns lime water milky. c. It is commonly said that food acts as fuel in the body. See if the "products of combustion", water and carbon dioxide, can be detected in the air breathed out. Test as follows : (1) Breathe on a cold pane of glass. Does moisture collect ? (2) Breathe through a glass tube or a lemonade straw into lime water. Do we breathe out carbon dioxide ? When the word combustion is used, it ordinarily means burning, that is, the union of a substance with the oxygen of the air with such rapidity that both heat and light are produced. But in order to have this combustion take place, it is necessary to have something more than a combustible substance and oxygen. Wood is a combustible substance, but it does not burn unless it is sufficiently heated to " take fire." Not all materials have to be heated to the same degree to make them burn, and the point to which each must be heated is called the kindling temperature of the substance. Phosphorus has a low kindling temperature and can easily be set on fire by the heat of friction ; that is why it is used on the heads of matches. Most combustible substances contain both carbon and hydrogen as well as a little oxygen. When they are burned in the air the carbon unites with the oxygen to make carbon dioxide, and the hydrogen with oxygen to form water, oxygen from the air being used in the process. The common fuels are inexpensive substances which are largely composed of these three elements. Foods, too, contain the same elements in large amounts. When food is burned in the body the process is a much slower one than ordinary burning and no light at all is produced, but the heat maintains the body temperature. Some fuels, like some foods, have nitrogen in them, but this does not help in the production of heat. The elements in fuels and foods are put together so differently, however, that they are entirely unlike in their nature, and the body could not burn coal or wood instead of food.

Food study