Examine the hydrogen in one of the
Fig. 42.
bottles. Has it color or odor? Holding the mouth downward thrust a lighted splinter into another bottle. The splinter does not continue to burn in this gas but the gas itself burns. Place another bottle mouth up on the table and allow it to stand for several minutes. Insert a lighted splinter. Why is not the hydrogen still present?
Draw out a glass tube so that the bore will be about as large as the point of a pencil and insert it in the rubber delivery tube. Pour more acid into the bottle and after this has been working for several minutes touch a lighted match to the glass tip of the rubber delivery tube. A jet of burning hydrogen will be formed. Hold a cold dry beaker over this burning jet. Water drops will collect in the beaker. The hydrogen is combining with the oxygen of the air and water is being formed.
Pure water is a chemical compound of two gases, hydrogen and oxygen. The oxygen we have always been familiar with, as it makes up about one fifth of the air by which we are surrounded. The hydrogen was prepared in the previous experiment. It is a colorless transparent gas, the lightest of all substances, and must be handled carefully. If it is mixed with oxygen or air and the mixture ignited, it explodes with much violence, forming water.
Experiment 37. -Fill a small beaker with fresh water. Heat it slowly. Bubbles collect on the bottom and sides. When the water becomes cold these bubbles do not disappear. If they were steam, they would change back to water. What are they? Where did they come from? Does water contain dissolved air? How can water animals that do not come to the surface obtain the air they need?
Experiment 38. -Put a piece of ice in water. What part of its volume sinks below the surface of the water? Is it heavier or lighter than water? From Experiment 24 do you conclude that cold water is heavier or lighter than warm water?
The water that we usually see has air and other substances dissolved in it, for water is the greatest solvent known. Another property of water which is very important is its practical incompressibility. Nomatter how much pressure may be put upon water its volume is little decreased and its density little changed. So it happens that substances which readily sink in the upper part of the sea sink to the bottom no matter how deep the water may be, as the bottom is so little denser than the top.
The substances that are dissolved in water mix thoroughly together. In isolated bodies of water there are often great differences in the amount and kinds of dissolved materials, but over the whole ocean from top to bottom the composition of the water is practically uniform.
From previous experiments we have learned some of the chief physical properties of water, so perhaps we can understand the different effects that water and land have had upon the development and activities ofliving things upon the globe. Some water animals move aboutCORALS.
These are fixed animals whose food is brought to them in solution by the ocean currents.
easily to get their food, but others have it brought to them in solution and so obtain it without muscular effort. The air that they breathe is in solution and they cannot as easily obtain a large quantity of it as can the land animals. Since the energy of all animals depends upon the amount of oxygen they use in their bodies, the water animals are generally less energetic than the land animals. Since they also have such an easy time in moving or floating about to get the things they need they have not developed as high organisms as the land animals.
Water is readily moved by the winds and becomes a means of cutting down the land and carrying away its material. When heated by the sun or any other source of heat it evaporates and, rising into the air, floats away to be condensed and to fall as rain or snow. It takes a great deal of heat to evaporate water and all this heat is given off when it condenses. Water seeks the lowest place it can find, giving out energy as it flows. In fact, the earth has been likened by some writersto a water engine, since water has played such an important part in its history.
Another property of water which is of great importance is its power to take up heat. This was shown in Experiment 27. When it cools, it gives out the heat it took up when its temperature was raised. It is for this reason that hot water bags are used to keep people warm, and that farmers sometimes in winter, when they fear that their cellars will freeze, carry down tubs of water to keep their cellars above the freezing point. This is why orange groves are often irrigated just before there is danger of a heavy frost.
A pound of water in cooling one degree gives out about as much heat as a pound of iron in cooling 9 degrees. This capacity for holding heat makes bodies of water warm up slowly in the summer and cool off slowly as winter approaches. As they cool they give back to the air the heat they have taken up. During the early part of the summer the air above them is kept cool and in the fall it is warmed. This property of water will be found later to be of great importance.
40.Materials Composing the Land.
Experiment 39. -Obtain specimens of the igneous rocks, lava, obsidian, basalt, granite; of the sedimentary rocks, sandstone, fossiliferous limestone, conglomerate, peat; of the metamorphic rocks, shale, schist, marble, anthracite coal. Examine these carefully with the eye and with the lens, noting whether they have a uniform composition or are made up of different particles. Are the particles composing the rocks crystalline? Are they scattered irregularly or arranged in layers? Test with a file or knife-blade the hardness of the rock as a whole and of its different constituents. Try a drop of hydrochloric acid on the different rocks to see whether they are affected by it. Describe in a general way the characteristics of each specimen.
