The water rises in the bottle because ⅕ of the air is used up by the burning candle. Air is ⅕ oxygen and ⅘ nitrogen. The oxygen unites with the burning gas of the candle and produces water vapor (H_{2}O) and carbon dioxide (CO_{2}); the nitrogen takes no part in the burning. [Illustration: FIG. 96 WATER FROM FLAME ] The water vapor (H_{2}O) condenses to water on cooling and takes up very little space. The carbon dioxide remains a gas and occupies space, but this is offset by the volume of the air which escaped at first. The result is that the volume of gas at the end is about ⅕ less, and the atmospheric pressure on the water in the pan lifts water into the bottle. The candle goes out because it must have oxygen to burn and the oxygen is used up. Experiment 72. Water produced by fire. It is certainly magic to produce water from fire, but you can do it easily as follows: Hold a clean, dry, cold tumbler over your alcohol lamp flame (Fig. 96). Does water deposit in the form of mist on the inside of the tumbler? [Illustration: FIG. 97 ATMOSPHERIC PRESSURE ] Repeat with fresh tumblers with the flame of a kerosene lamp and of a candle. Are the results similar? Direct the blowpipe flame into the end of a piece of No. 2 or 4 tubing. Does water deposit in drops inside the tube about 1 inch above the end? The “why” of it One of the chief constituents of alcohol, kerosene, and candle wax is hydrogen (H), and when this burns in the oxygen (O) of the air, it produces water (H_{2}O). It is this water which condenses on the cold glass. MAGIC WITH AIR Experiment 73. Atmospheric pressure. Arrange a No. 6 tube as in 1, Fig. 97, and suck air out at the top. Does the water run uphill into your mouth? Hold your finger over the top and lift the tube out of the pail (2). Does the water remain in the tube? Fill a bottle with water to overflowing, insert a No. 2 tube into your one-hole stopper, insert the stopper into the mouth of the bottle (3) without admitting air below the stopper, and try to suck water out of the bottle. Do you find that you cannot do so? [Illustration: FIG. 98 WATER DRIVEN UP TUBE BY ATMOSPHERE ] Repeat (3) with the bottle half full of air (4). Do you find that you can now suck part of the water out of the bottle, and all of it if you admit air? The “why” of it The atmosphere which surrounds the earth exerts a pressure of 15 pounds per square inch on everything at the earth’s surface. It exerts this pressure equally downward, sidewise, and upward. It is this atmospheric pressure on the water in the pail (1) which lifts the water into the tube when you decrease the pressure on the water in the tube by sucking out air and then water. It is this pressure upward that supports the water in 2. The water does not rise in 3 because the atmosphere cannot exert pressure downward on the water in the bottle. [Illustration: