Chapter IV

CLASSIFICATION OF THE ELEMENTARY SUBSTANCES.

In speaking of the elementary substances some of them have been referred to as metals. What then is the exact idea conveyed by this designating term? Everyone can readily picture in his mind some metal or metals like gold, silver, tin, zinc and others that have certain common characteristics, such as great weight, and the peculiar brilliancy and power of reflecting light which is described as metallic lustre. Another well marked and widely recognized characteristic at once thought of is the facility with which the substances ordinarily known as metals maybe beaten or rolled into thin layers. This property, called malleability, (a word derived from the Latin word _malleus_, a hammer,) is not possessed in any striking degree by substances other than metals. Thus sulphur is not malleable: quite the contrary, it is very brittle. Charcoal, which consists mostly of the elementary substance called carbon, is likewise not malleable; neither of these last two substances would be likely to be considered by even an ordinary observer as metals. In fact they are classed as non-metals by the chemist. This division of the elementary substances into metals and non-metals is dwelt upon, not because it can be called a very important one, but because it is widely used in works on chemistry and because in deciding to which of these two classes a given substance belongs, ultimate dependence must be placed upon its chemical characteristics rather than upon its mere mechanical properties.

The Meanings Associated with the Term Metal.

The principal properties referred to are best presented in three groups.

_First. Metallic Properties Associated with Mechanical Relations._

An elemental substance accepted as a metal must possess the property of existing in a solid condition; a weight rather greater than that of most well-known substances; considerable hardness, malleability, ductility (that is the capability of being drawn out into fine wire).

_Second. Metallic Properties Associated with Physical Relations._

A metal should possess the metallic lustre; the power called opacity, by reason of which it does not allow light to pass through it; the noticeable capability of allowing heat to flow in it, called the power of conducting heat; the ready capacity for allowing the electric current to flow in it, called good conducting power for electricity.

_Third. Metallic Properties Associated with Chemical Relations._

A metal should possess the power and the tendency to readily form a chemical union with oxygen; the chemical power to act upon compounds containing hydrogen, in such a way as to turn the hydrogen out, and take its place in the old compound and thus form a new one; the relationship towards the electric current such that when the element is subjected to the galvanic battery, it tends to gather about the negative pole—in consequence of which characteristic it is usually called electro-positive.

But while no known metal appears to possess the entire range of properties with which in thought the ideal one is endowed, every substance classified as a metal should possess many of them.

An illustration of what has been said may be found in metallic mercury. From the fact that under ordinary conditions it is a liquid it is plain that mercury must lack certain of the metallic properties referred to; that is, it does not possess the solid form, it does not possess hardness, it does not possess malleability, it does not possess ductility. Yet if it is cooled to a low temperature—about forty degrees below zero—it freezes, in other words becomes solid; then it possesses many of the distinctly metallic features that it necessarily lacks when in the ordinary liquid condition. Of course this liquid condition is a mere incidental circumstance, due to the temperature which ordinarily prevails upon our earth. If our ordinary temperature were slightly lower than forty degrees below zero, mercury would then be commonly known as a solid, hard, lustrous, heavy, malleable metal—capable of course of melting with a slight accession of heat.

As a further illustration, in a somewhat different direction, mention may be made of the metal lithium. This substance cannot be called heavy, since it is lighter than water; indeed it is the lightest solid known. But on the other hand it possesses in a striking degree those chemical features of metals, such as strong affinity for oxygen and tendency to combine with it, which have already been detailed in our definition of the ideal metal.

The Term Non-metal.

The term non-metal is suggestive of a negative idea, and not of any definite or positive one. In fact it is intended to intimate that elementary substances of this class are those which do not properly belong to the other. Sulphur and carbon have been already alluded to as examples of non-metals; other non-metals, such as oxygen, hydrogen, nitrogen and chlorine among the gases, bromine, a liquid, and iodine, antimony, phosphorus among solids, are far less familiarly known to most persons.

READING REFERENCES.

Elements, Classification of
=Williamson=, A. W.—Jour. of Chem. Soc. of London, xvii, 211.

Chemical Theory.
=Cooke=, Josiah P., Jr.—The New Chemistry. New York. 1874.
=Remsen=, Ira.—Principles of Theoretical Chemistry.
Philadelphia. 1883.
=Tilden=, William A.—Introduction to the Study of Chemical
Philosophy.
=Wurtz=, Ad. (Henry Watts, Tr.)—History of Chemical Theory.
London. 1869.