Experiment 59. -Get two or three bottles of carbon dioxide from the chemical laboratory, or prepare it by pouring dilute hydrochloric acid upon pieces of limestone in a bottle and collecting the gas over water. Does the appearance of this gas differ in any way from that of air? Smell of one of the bottles that has stood over water for some time. The gas has no odor. Plunge a lighted match into one of the bottles containing the carbon dioxide. What happens? Does the gas burn or support combustion? Slowly overturn a bottle of the gas above a lighted candle. The candle is extinguished. The gas falls out when the bottle is overturned, thus showing that it is heavier than air. If the amount of carbon dioxide in the air were largely increased, what effect would it have upon combustion?
Animals smother in carbon dioxide. It is known to coal miners as choke damp, because frequently after they have escaped from an explosion they are smothered by it. It occurs at a few localities, as at the Dog Grotto near Naples and in Death Gulch, Yellowstone National Park, in sufficient quantities to be fatal to animals passing through these places.
As a rule, however, the proportion of oxygen, nitrogen and carbon dioxide is the same for all places on the surface of the earth and it is only where for some peculiar cause carbon dioxide is emitted fromthe ground in a place sheltered from the wind, that it can accumulate. As animals and men breathe it out, rooms where they stay must have proper ventilation.
The nitrogen is needed to dilute the oxygen. If oxygen were undiluted, animals could not live, and a fire once started would burn up iron as readily as it now does wood. As has already been stated, certain bacteria take nitrogen from the air and prepare it so that plants can use it.
Plants and animals both need water vapor. Were it not for this form of moisture there would be no rain, and without rain life could not exist. Thus the air which contains oxygen and water vapor for both plants and animals, carbon dioxide for the plants, and nitrogen to dilute the oxygen, is one of the greatest factors in the life history of the earth.
52.Weight of Air.
Experiment 60. -Into a fivepint bottle insert a tightly fitting rubber stopper through which a glass tube extends. To the outer end of the glass tube tightly fit a thick-walled rubber tube of sufficient length for the attachment of an air pump. Put a Hoffman"s screw upon the rubber tube. See that all connections are air-tight. Weigh carefully the apparatus as thus arranged. Now attach the rubber tube to the air-pump and extract the air from the bottle. When all the air that can be exhausted has been removed, close the rubber tube tightlyFig. 5 1.
with the Hoffman"s screw and weigh again. Unclamp the Hoffman"s screw and allow the air to enter the bottle. The weight should be now the same as at first. Or, instead of weighing a bottle of air, weigh an incandescent light bulb. Make a hole in it with a blowpipe and weigh again. Is the weight now the same as before?
We have found by the previous experiment that air has weight. With the apparatus used it was impossible to tell exactly the weight of the air extracted or to determine the weight of a definite volume of the air. IfBALLOON.
The gas in the balloon is lighter than air, so the balloon floats in air as a piece of wood does in water.
we had been able to do this, we should have found that on an average day, at sea level, the weight of a liter, a little more than a quart, of air, is about 1.2 grams. 12 cu. ft. weigh about 1 lb. The air extends to so great a height that although very light, the weight of so great a mass of it is considerable.
Now that air has been found to have weight, it can be seen why a light body like a balloon will float in it in the same way that a stick will float in water. The weight of the air varies with the pressure and temperature, as we shall find later.
53.Expansion of Air when Heated. -Air expands very muchwhen heated, as was seen in Experiment 17. It is found that if air at freezing is heated to the temperature of boiling water, it will expand about 4/11 of its volume. The force with which air expands is so great that sometimes when buildings are on fire and there is no opening for the confined air to escape, the walls are blown out or the roof blown off by the expansion of the hot air, and great injury done to those fighting the fire. That air expands upon being heated is readily seen when a toy balloon is brought from the cold outer air into a hot room, -the cover- ing begins at once to tighten and the balloon to swell.
54.Weight of Air as Affected by Heat and Cold.
Experiment 61. -Take two open flasks of nearly the same weight and capacity and balance in as nearly a vertical position as possible at the ends of the arms of a beam balance. Bring the flame of a Bunsen burner to the upper side of the bulb of one of theFig. 52.
flasks so that the hot air currents that are generated will have no upward push on the flask. Do not allow the hot air to get under the flask. What is the effect?
As the previous experiment shows, and as we should expect from the fact that air has been found to expand when heated, it follows that hot air is lighter than cold air. A liter of air at freezing under ordinary pressure weighs about 1.293 grams, but at the temperature of boiling water it weighs only about .946 grams. So a volume of cold air, being heavier, will exert more pressure at the surface of the earth than an equal volume of hot air.
As air is a gas whose particles can move freely among themselves we should expect that a heavier column of cold air would sink down and distribute itself along the surface under surrounding lighter air just as a column of water falls when its supports are withdrawn and forces up the lighter air which surrounds it.
A similar action is seen when water is poured upon oil; the watersinks to the bottom and forces the
oil to rise. Thus if air is heated at any place, we should expect that thereHOT AIR FURNACE.
The hot air rises through the pipes and registers, and cold air presses in from outside.
