ELEMENTARY CHEMISTRY.

THE earth is made up of a variety of solid, liquid, and gaseous materials. Chemistry investigates the relationship between the different kinds of atoms or particles of which these materials are composed. If the earth were composed of only one simple substance, there could be no such science as chemistry.

All substances, whether animal, vegetable, or mineral, are either simple or compound. Those which cannot be reduced into any simpler form are called elements, and these elements combine to form an infinite variety of compound bodies. We may illustrate this by the letters of the alphabet, which cannot be separated into any simpler form, but by different combinations form a great variety of words. These words can be separated into their letters, as can the compound bodies into the elements of which they are composed. It is only compound bodies which can thus be separated. Sulphur, iron, zinc, copper, oxygen, hydrogen, cannot be resolved into any simpler substance: they are therefore called elementary bodies. Water can be separated into oxygen and hydrogen, and water is therefore a compound body,

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and not an element, as was once supposed. Again, chalk, or carbonate of lime, is made up of three elementary bodies, a metal called calcium, oxygen, and carbon. Common salt is composed of two elementary bodies,—a metal called sodium, and chlorine. The great majority of compounds are formed by the union of two, three, or four elementary bodies. The separation of these compound bodies into simpler forms is called analysis, and the formation of compound bodies by the union of simple ones is called synthesis.

The Elementary bodies are sixty-two in number; but many of them are so rare as not to require special attention. They are divided into metals and metalloids, or non-metallic bodies. The metals have great lustre : are good conductors of heat and electricity. These properties are never associated in a non-metallic body. This division is not based on any exact principles of science, but as a common means of description. The metalloids or non-metallic bodies in the following table are marked with an asterisk.

The rare elements are distinguished by italics, and the figures to the right represent the combining equivalent or atomic weights of these elements. The figures in the second column will be explained under the section on weight.

Some of the elements have a popular name: sulphur is called brimstone; mercury, quicksilver. Carbon when crystallised is a diamond; when prepared artificially, it is known as charcoal, coke, lamp-black, and bone-black. The Latin names of all the metals terminate in um. Five of the elementary bodies are gaseous under ordinary pressure and temperature; -hydrogen, oxygen, nitrogen, chlorine, and fluorine. Two are liquid,—mercury and bromine. The others are solid. The elementary bodies are represented by symbols. These symbols are of great importance in expressing chemical changes.

The student should learn the symbols and combining equivalents of the commonly occurring elements.