The student starts by measuring the volume of a rectangular solid, then progresses to measuring the volume of a stack of coins, a quantity of water, and an irregular solid. From this experimental work, the law of conservation of mass emerges naturally. In the other physical-science books that I have seen, it is simply declared as if it were a sacred commandment. The concept of a chemical element arises from the student's laboratory work, with some help from the book's skillful authors. It is instructive to compare their approach with the one used in a conventional book, Prentice Hall's Chemistry of Matter .
Elements are the simplest type of substance.
Elements are made of only one kind of atom. . . . Atoms of elements combine with one another to produce new and different substances called compounds. . . . The combining of atoms of elements to form new substances is called chemical bonding. In Introductory Physical Science , however, we find real science instead of priestly pronouncements. The student, during his laboratory work, has weighed a sample of sodium chlorate, has heated it and weighed it again, has inspected the substance produced by the heating, and has compared that substance with the starting material.