This mineral matter gives the body the mineral salts which it needs; but in addition to this, most people desire and eat a considerable quantity of common salt every day. The amount eaten is far in excess of the sodium and chlorine the body requires, though sodium is an important constituent of many of the fluids of the body, and chlorine is found in hydrochloric acid of the gastric juice, the digestive fluid of the stomach. A great diversity of opinion exists as to the desirability of much salt in the diet, but the balance of evidence indicates that a liberal amount of salt is not harmful, but rather beneficial.

Experiment. To show the mineral part of bones, place a moderate sized bone on a hot coal fire for half an hour or longer.

To show the gelatinoids of bones, place a small bone in a shallow dish and cover with strong vinegar or weak hydrochloric acid (muriatic acid) and let stand over night or longer. The acid will dissolve out the phosphate of calcium leaving the animal matter.

Coffee, an important part of the breakfast to most people, introduces an important feature of the chemistry of cooking-the production of the proper flavor. The chemical changes involved are too subtile for explanation here—indeed many are not understood. The change in the coffee berry by roasting is a familiar illustration. The heat of the fire causes the breaking up of a substance existing in the berry, and the formation of several new ones. If the heat is not sufficient,

Flavor

Production

the right odor will not be given; if it is too great, the aroma will be dissipated into the air, or the compound will be destroyed.

Broiling steak is another illustration—a few seconds too long, a few degrees too hot, and the delicate morsel becomes an irritating mass. The chemistry of flavorproducing is the application of heat to the food material in such a way as to bring about the right changes and only these. Flavors in addition to the pleasure they give to eating have the advantage of stimulating the flow of digestive fluids and making digestion more

easy.

DECAY

The clearing away of the breakfast introduces to the housekeeper two important problems:-(1) the preservation of the remaimag food from decay; (2) the proper cleaning of the articles used during the meal and its preparation.

Decay is caused by minute vegetable organisms known as moulds and bacteria. Both are present in the air either as the plants themselves or as their spores, the reproductive cells, ready to grow whenever they fall upon suitable soil. When these grow upon animal or vegetable substances, a variety of new compounds are formed, many of them taking oxygen from the air, so that finally the carbon becomes carbon dioxide, the hydrogen is oxydized to form water, and the other elements in their turn also become oxides, so that the decaying substance is utterly destroyed and

new substances made in its place. When organic substances are protected from the action of these living plants, decay will not ensue.

The old idea was that oxygen caused decay, but many experiments disprove this. Oxygen alone does. not produce this result, but oxygen with "germs" will do so. These "germs" develop much more slowly in the cold, so that food is placed in the refrigerator or in a cool place and away from the dust.

The problems introduced by these living plants, their life history and their work, as well as the methods of prevention and care against their ravages, belong rather to household bacteriology than to chemistry. We are ready therefore to pass on to our next problem, that of cleaning.

Decay Not
Caused by
Oxygen Alone

CHEMISTRY OF THE HOUSEHOLD.

PART L

Read Carefully. Place your name and address on the first sheet of the test. Use a light grade of paper and write on one side of the sheet only. Do not copy answers from the lesson paper. Use your own words, so that your instructor may know that you understand the subject. Read the lesson paper a number of times before attempting to answer the questions.

I.

2.

What do you understand a "chemical element" to be? Name all that you have ever seen.

What is a "saturated solution?"

Name the substances usually found in the house which are soluble in water.

3. What causes atmospheric pressure? Explain some effects of it.

4.

Why must the diet of animals include fresh air? 5. Explain the effect of cooking on starch. (b) On fats. (c) On proteids.

6. What are the products of combustion in burning coal or wood?

7. What is meant by "conservation of matter?"

8. How can the boiling point of water be raised? How may it be lowered?

9. What is meant when it is said that a chemical substance always has the same composition?

IO.

II.

What is "latent heat?"

What can you say of the composition of meat? 12. Explain the physical and chemical changes which starch must undergo before it is absorbed into the circulation.

13.

What can you say of the chemistry of breadmaking?

14. Why is distilled water pure?

15. Explain the composition of water.

16. Describe the chemistry of a sulphur match.

17. How is charcoal prepared? How is coke made? 18. Why does the proportion of carbon dioxide in the atmosphere not increase?

19. In what different ways is food used in the body? 20. Do you understand all parts of this lesson paper? If not, what part is not clear?

NOTE.-After completing the test sign your full name.