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light as well as some direct sunlight. A corner room is best if it can be obtained. If tables are used, they should be arranged so that each student may get as much light as possible without shading his neighbor.

INSTRUMENTS USED. - Every pupil ought to provide himself, in addition to the laboratory notebook and a hard pencil, with the following articles: a hand lens (a small brass-mounted tripod lens, one mounted in vulcanite, or the small lens known as a linen tester), two or three darning needles mounted in clder pith or in wooden handles, a good eraser, and a ruler marked with the metric system. A small pair of forceps, scissors, and a light, thinbladed knife or scalpel are useful, but not essential for most laboratory work.

INTEREST IN LABORATORY WORK ESSENTIAL. It is not, however, the laboratory or the equipment that makes the laboratory work a success. It is rather the spirit of the pupils. Interest in the work is the first essential. When at work on what may seem to be only dry details, lcok ahead and think about what you are doing. Try to find a purpose in everything that you do. It is possible to make any piece of biological work interesting by keeping in mind that everything in nature is part of a great plan and has a purpose. It is your place to find out just how the given part that you may be studying is fitted or adapted to its work in the general plan.

At the end of each of the following chapters is a list of books which have proved their use either as reference reading for students or as aids to the teacher. Most of the books mentioned are within the means of the small school. Two sets are expensive one, The Natural History of Plants, by Kerner, translated by Oliver, published by Henry Holt and Company, in two volumes, at $11; the other, Plant Geography upon a Physiological Basis, by Schimper, published by the Clarendon Press, $12; but both works are invaluable for reference.

Two books stand out from the pedagogical standpoint as by far the most helpful of their kind on the market. No teacher of botany or zoology can afford to be without them. They are: Lloyd and Bigelow, The Teaching of Biology, Longmans, Green, and Company, and C. F. Hodge, Nature Study and Life, Ginn and Company. Other books of great value from the teacher's standpoint are: Ganong, The Teaching Botanist, The Macmillan Company; L. H. Bailey, The Nature Study Idea, Doubleday, Page, and Company; and C. B. Scott, Nature Study and the Child, D. C. Heath and Company.

II. INTRODUCTORY EXPERIMENTS IN CHEMISTRY AND PHYSICS

In

In the introductory chapter we learned that science concerns itself with matter, and that the science of biology is concerned with the study of this matter when it is in a living state. order to understand this definition we must first get a conception of what matter really is.

Matter. If you take a piece of ice in your hand, you are aware that it is cold, and that it has weight and a certain form. We call it a solid. A few minutes' exposure to the warmth of your hand will change this solid into a liquid. If the water thus formed be heated over a flame until it boils, it may be changed again, this time into a gas which passes off into the air and becomes invisible. The ice has successively changed from a solid to a liquid and then to a gas. In each state we could measure it and weigh it. In each form it occupies space. It must be considered matter, whether in the form of a solid, a liquid, or a gas.

Physics and Chemistry. The sciences which treat chiefly of the properties and forces of inorganic or dead matter, and of the relations of the parts of the substances composing it, are known as the sciences of physics and chemistry.

Chemical Element All the building materials of this universe, both living and lifeless, are classified by chemists as either chemical elements or chemical compounds. A chemical element is so simple in its structure that it cannot be broken or decomposed into a simpler substance. Examples of such substances are oxygen, making up about one fifth of the atmosphere; nitrogen, composing nearly all the remainder of pure air; carbon, an element that enters into the composition of all organic living things or those that once possessed life; and over sixty others of more or less importance to us in the study of biology.

Preparation of Oxygen.

Oxygen may be easily prepared in the schoolroom or at home in the following manner.1 Heat half a teaspoonful of black oxide of manganese with a little more than its bulk of chlorate of potash in a test tube over a bunsen flame or a spirit lamp. Vapors will be seen to arise as the mixture becomes heated. After a moment insert a glowing match into the mouth of the test tube; a burst of white flame results. In what form does oxygen pass off from the two chemicals in the test tube? How could you determine the presence of oxygen in a substance?

Preparing oxygen.

Properties of Oxygen. The physical properties of oxygen are those which we determine with our senses. Oxygen, when carefully prepared, is found to be a colorless, odorless, and tasteless gas. It is known to form nearly one half of the earth's surface, to form eight ninths of all water and over three fourths of the weight of the plants and animals inhabiting this world of ours. It has the very important chemical property of causing things placed in it to burn. If, for example, a piece of picture wire is heated red-hot, and then placed in a jar of oxygen, the metal will burn with a bright flame.

Oxidation. Light carefully a small piece of magnesium wire and then place it in a test tube in which you have previously made oxygen. Notice the very brilliant flame. A light-colored ash remains. This is magnesium oxide. In the above experiment the oxygen in the test tube unites with the magnesium so rapidly as to form a flame. This process is known as a combustion.

The chemical union of oxygen with any other substance is called oxidation. Can you distinguish between combustion and oxidation? Oxidation takes place wherever oxygen is present. These facts, as we shall see later, have a far-reaching significance in the understanding of some of the most important problems of biology.

Oxidation in a Match. -The simple process of striking a sulphur match gives us another illustration of this process of oxidation. The head of the match is formed of a composition of phosphorus, sulphur, and some other materials. Phosphorus is a chemical element distinguished by its extreme inflammability. I unites with oxygen at a comparatively low temperature. Sulphur is another chemical element that combines somewhat easily with oxygen but at a much higher temperature. The rest of the match head is made up of red lead, niter or some other substance that will release oxygen, and some glue or gum to bind the materials together. The heat

1 For a concise statement of this and following experiments in the scientific form expected from the pupil, see Hunter and Valentine, Laboratory Manual of Biology, Henry Holt and Company, pages 213 ff.

caused by the friction of the match head against the striking surface is enough to cause the phosphorus to ignite; this in turn ignites the sulphur and finally the wood of the match, composed largely of the element carbon, is lighted and oxidized. If we could take out the different chemical elements of which the match is formed and oxidize them separately we should find that the amount of heat needed to start the oxidation of the substances would vary greatly. The element phosphorus, for example, is kept under water in a glass jar because of the extreme readiness with which it unites with oxygen.

Experiment.-Oxidation may take place with very little heat present, although heat is always a result of oxidation.

Place an iron nail in a bottle of water, and cork and seal the bottle. Place another nail in a saucer in which

is kept a little water. Note the formation of rust on the nail in the saucer and the absence of rust on the nail in the bottle. Rust is iron oxide and is formed by the union of iron and oxygen. This kind of oxidation

is said to be a slow oxidation. Slow oxidations are constantly taking place in nature and result in the process of decay and breaking down of complex materials into simpler materials.

Hydrogen &
Carbon,
in wood

Oxygen in the air

E

Carbon dioxide

In the smoke

Diagram of combustion or rapid oxidation in a stove.

-

One of the most im

Heat given off as result of Oxidation. portant effects of oxidation lies in the fact that, when anything is oxidized, heat is produced. This heat may be of the greatest use. Coal, when oxidized, gives off heat; this heat boils the water in the tubes of a boiler; steam is generated, wheels of an engine turn, and work is performed. The energy released by the burning of coal may be transformed into any kind of work power. Energy is the ability to perform work.

Carbon. Another chemical element of much importance to us is carbon. This element makes up an important part of all things that now have or at any time had life. Such matter we call organic. Carbon is found making up part of the bodies of plants and animals, of coal, and in a nearly pure state in the diamond. The presence of carbon can often be detected by the fact that the substance containing it turns black upon being heated in a flame.

Experiment. Heat separately on a tin plate some leaves, sticks of wood, gravel, sand, and rich black earth. Place them over a hot flame for some minutes. Which of the above materials contains carbon?

If some substance that contains carbon, as a piece of wood, is burned in a jar with a tight-fitting cover, the flame will be seen to go out after a short

HUNTER'S BIOL. 2

time. This will occur before all the wood is consumed. Another splinter of wood, placed in a jar with the cover off, will burn slowly but completely. A third piece of wood burned in the air will be quickly and completely consumed. If now a little limewater' is poured into the jar which was closed, and the contents shaken up, the limewater will be found to turn a milky color. This milky appearance is due to the formation within the jar of a material known as calcium carbonate. This is thrown down in the liquid as a result of the union of carbon with lime. Evidently some of the carbon from the wood has passed in the form of a gas into the limewater and there united with the calcium in the lime. Remembering what we know about oxidation, we see that the carbon of the wood has passed off and united with oxygen of the air in the jar. Thus, by the uniting of the two chemical elements, a chemical compound has been formed. The presence of carbon dioxide is known by the fact that it puts out a flame and that it turns limewater milky. This compound is known to chemists as carbon dioxide.2

Apparatus for separating water into the two elements hydrogen and oxygen.

Nitrogen. There is another gaseous substance that will not support combustion; this is the element nitrogen. Its presence in the atmosphere is shown by the following experiment:

Invert a bell jar in a large, deep dish of water, having previously placed within the jar on the surface of the water a piece of phosphorus supported on a flat bit of wood or cork. Leave the experiment for at least two days undisturbed (or, the phosphorus may be lighted and then the jar left for a few hours untouched). After that time the water will be found to have risen considerably in the jar.3 If you make a mark on the cover

1 Limewater can be made by shaking up a piece of quicklime the size of your fist in about two quarts of water. Filter or strain the limewater into bottles and it is ready for use.

2 Chemists have shown that any given structure is made up of molecules. A molecule is the smallest bit of matter that can exist separately and still retain its composition and properties. A molecule is composed of still smaller particles calle atoms. Carbon dioxide is so called because its molecule is made up of one atom of carbon and two atoms of oxygen. It is customary to use certain letters or symbols to designate certain chemical elements, as C for carbon, H for hydrogen, N for nitrogen, P for phosphorus, Fe (Latin ferrum) for iron. The molecule of carbon dioxide is made of one part of carbon and two of oxygen; it is written CO2. This is called the chemical formula. If an electric current is passed through a jar of water, the contents will be broken down into the elements hydrogen and oxygen. If now the gases are carefully collected, there will be found to be exactly twice as much of the hydrogen gas as there is of the oxygen. The chemical formula for water is H,O. See figure.

It would be well for the teacher at this place to bring up the subject of atmospheric pressure. Air presses down on the earth's surface at sea level with a weight of fifteen pounds to every square inch of surface.

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