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 force, electricity, sound, friction, density, weight, and the like.

Chemistry is the science that treats of the composition of matter. All matter is made up, as we have seen, of elements. Very few elements exist in nature in a free or uncombined form. The nitrogen and oxygen of the air are the leading uncombined elements.

In order to express the chemical combinations clearly, symbols are used to represent each element, and these symbols are then combined to represent the proportions of each in the compound. If C stands for carbon and O for oxygen, the carbon dioxid might be represented by the formula COO. In order to avoid the repetition of any letter, however, a number is used to denote how many times the element is taken: thus the formula always used for carbon dioxid is CO_{2}. The formula for hydrogen oxid, or water, is H_{2}O; that for starch is C_{6}H_{10}O_{5}. N stands for nitrogen; P, for phosphorus; K, potassium; Fe, iron; S, sulfur.

Biology is the science that treats of life; that is, of all knowledge of plants and animals of all kinds. (See page 1, "Animal Biology.")

Some of the foregoing suggestions may be readily explained and illustrated by simple experiments with a burning candle. The following directions for such experiments are by G. W. Cavanaugh.

The materials needed for this exercise are: a piece of candle about two inches long, a lamp chimney (one with a plain top is best), a piece of white crockery or window glass, a piece of fine wire about six inches long, a bit of quicklime about half the size of an egg, and some matches. All of these, with the possible exception of the quicklime, can be obtained in any household.