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Caution: If in 3 below an explosion occurs, collect another bottle of hydrogen before answering the questions, for an explosion indicates that oxygen is mixed with the hydrogen, and such a mixture is dangerous to experiment with.

1.

Examine a bottle of hydrogen, and state whether hydrogen is a solid, a liquid, or a gas. Compare its color with that of oxygen and carbon dioxid.

2. Thrust a lighted stick up into the mouth of an inverted bottle of hydrogen. (This experiment will be more satisfactory if the room is darkened.)

a. State what was done and tell how the hydrogen affected the burning stick.

b. How does the burning stick affect the hydrogen?

c. What is one difference between oxygen and hydrogen? d. What is one difference between hydrogen and carbon dioxid?

3. If hydrogen is not being given off from the delivery tube in sufficient quantity, pour into the thistle tube some hydrochloric acid. Detach the delivery tube from the rubber tube of the hydrogen apparatus and insert in its place a piece of glass tubing, the upper end of which is drawn out to a small diameter. Collect some of the gas in a test tube by displacement of air and light it. When it burns with only a slight puff, apply a lighted match to the hydrogen escaping from the drawn-out tube.

Hold over the flame a bottle which is clean and dry.
a. Describe the preparation of this experiment.
b. What do you find on the inside of the glass?

c. What, therefore, is formed when hydrogen burns? 4. When hydrogen burns, it unites with the oxygen of the air and forms oxid of hydrogen, more commonly known as water (formula, H2O).

a. In what respect does hydrogen differ from oxid of hydrogen (water) in its most common form?

b. State how oxid of hydrogen was formed.

c. In what respects is the method of producing oxid of hydrogen (water) the same as that of producing oxide of carbon (carbon dioxid)? (See 11, 5 above.) 5. Name five characteristics of hydrogen.

13. Nitrogen (symbol, N) and the composition of the air. - Laboratory Study No. 5. Demonstration.

Fasten a candle to a piece of cardboard and float the latter on a tray of lime water. Light the candle, and cover the flame with an inverted wide-mouthed bottle, bringing the latter slowly down until the edge rests on the bottom of the tray. Allow the candle to burn as long as it will. Then turn the bottle right side up, covering the mouth with the cardboard, keeping inside the bottle the lime water that has risen to take the place of the oxygen. Shake the contents of the bottle, to make the lime water absorb the carbon dioxid, and allow it to stand till the upper part of the jar is clear. Keep the bottle covered to prevent the mixing of air with the nitrogen.

1. Examine a bottle of nitrogen. Is it a solid, a liquid, or a gas? What is its color?

2. Thrust a burning splinter of wood into the nitrogen.

a. Tell what was done. Does the wood continue to

burn?

b. Does the nitrogen burn?

c. In what respect does nitrogen differ from oxygen?

3. State four characteristics of nitrogen.

4. Why does carbon burn faster in oxygen than in air? 5. Air consists principally of oxygen and nitrogen. The water in the bottle represents the amount of oxygen there was in the bottle of air, and the nitrogen occupies the rest of the space.

a. About what fractional part of the air in the bottle was oxygen?

b. What fractional part of the air in the bottle is nitrogen?

6. Expose to the air of the room for a half hour or more a dish with some clear lime water.

a. Describe the experiment, stating the effect on the lime

water.

b. What substance does this experiment prove to be present in air?

II. DEFINITIONS

14. A chemical element is a substance that has never been separated into two or more different kinds of matter.1 Over seventy of these elements are known at the present time, and of these seventy, twelve are found constantly in the living substance of plants and animals. The most common of these twelve elements are carbon (symbol, C), hydrogen (H), oxygen (O), nitrogen (N), sulphur (S), phosphorus (P), iron (Fe), and calcium (Ca), which is found in lime.

[In addition to the elements already studied (C, O, H, N), the others mentioned should be shown to students; and if time permits, some of these elements may be burned or oxidized in oxygen and the characteristics of the oxids thereby formed may be discussed.]

15. A chemical compound is a substance formed by the union of two or more chemical elements. - Two of the important compounds considered in biology are carbon dioxid (formula CO2), which means that it is composed of one part of carbon and two parts of oxygen, and water (formula H2O), which means that it is composed of two parts of hydrogen and one part of oxygen.

16. A mixture differs from a compound in the fact that the elements or compounds of which the former is composed are not chemically united. In air, for instance, the oxygen and nitrogen are not chemically combined, but are simply put together as one might mix pepper and salt. Again, when sugar is dissolved or mixed with water, the two compounds are mingled so closely that the sugar disappears; it may easily be obtained unchanged in its composition by evaporating the water.

1 There are, however, exceptions to this statement, but they are too technical for discussion in an elementary text-book.

17. Oxidation is the chemical union of oxygen with some other substance. It may take place slowly, as when carbon is made to glow in the air; or it may take place rapidly, as when carbon burns in oxygen. But whenever oxidation takes place, (1) an oxid is formed, (2) a certain amount of heat is liberated, and (3) if the process is sufficiently rapid, light is seen.

III. A STUDY OF THE FOOD SUBSTANCES

18. Introduction. The food substances needed by plants and animals may be divided into five classes, namely: (1) carbohydrates (i.e. starches and sugars); (2) fats and oils; (3) proteins, which are also known as albuminous or nitrogenous substances (e.g., white of egg, lean meat, gluten of wheat); (4) minerals (e.g. common salt, saltpeter, phosphate of lime); (5) water.

19. To determine the chemical composition of starch. Laboratory Study No. 6. Suggested as home work.

Warm some starch in an old cooking spoon in order to drive off any water that may be in it, but do not allow it to burn. To determine when the starch is free from water, hold the heated starch under a dry, cold tumbler, and if no moisture collects upon the tumbler, the starch contains no water. Now set the starch on fire, and hold a cold, dry glass over the burning starch.

1. Tell what you have done and state what is formed on the inside of the tumbler by the burning of the starch.

2. What is the only chemical element that could possibly form water by burning (i.e. by uniting with oxygen)? 3. What chemical element, therefore, must have been present in the starch in order to have produced water when dry starch is burned?

1 The term protein is used throughout this book instead of proteid, because of the unanimous recommendation in favor of the former term by the American Society of Biological Chemists and the American Physiological Society. See Science, April 3, 1908.

4. What substance is left in the cooking spoon after the flame goes out?

5. Name two chemical elements proved to be present in starch. 6. Starch also contains oxygen. Name now the three chemical elements of which this nutrient is composed.

20. To determine the chemical composition of sugar, fat, and protein. - Laboratory Study No. 7.

(Optional.)

1. Test sugar in the same way as directed in Laboratory Study No. 6, 1-5 (above).

a. Describe each of the experiments, giving results and conclusions.

b. Sugar, like starch, has oxygen also in its composition. Name now all the chemical elements of which sugar is composed.

2. In a similar way test a fat (e.g. lard, or the fat of meat). a. State what you do, what you see, and what you conclude. b. Fat, like starch and sugar, has oxygen in its composition, but in a different proportion. State, therefore, the three elements present in fat.

3. (Demonstration.) Secure a vegetable protein (e.g. gluten) and test it as directed above.

a. Describe your experiments and give your results and conclusions.

b. Besides the two elements you have shown to be present, protein also contains oxygen, nitrogen, sulphur, phosphorus, and often other elements. State, now, the chemical elements of which this food substance is composed.

21. Summary. The carbohydrates, as we have learned and as their name implies, are composed of the chemical elements carbon, hydrogen, and oxygen. The same three chemical elements are likewise present in fats and proteins, but in different proportions. Proteins, however, in addition to the carbon, hydrogen, and oxygen, contain at least three other

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