WHAT METALS ARE—CHARACTERISTICS AND GENERAL PROPERTIES OF METALS—CLASSIFICATION—SPECIFIC GRAVITY—DESCRIPTIONS.

We have learnt that the elements are divided into metalloids and metals, but the line of demarcation is very faint. It is very difficult to define what a metal is, though we can say what it is not. It is indeed impossible to give any absolute definition of a metal, except as “an element which does not unite with hydrogen, or with another metal to form a chemical compound.” This definition has been lately given by Mr. Spencer, and we may accept it as the nearest affirmative definition of a metal, though obviously not quite accurate.

Fig. 396.—Laminater.

A metal is usually supposed to be solid, heavy, opaque, ductile, malleable, and tenacious; to possess good conducting powers for heat and electricity, and to exhibit a certain shiny appearance known as “metallic lustre.” These are all the conditions, but they are by no means necessary, for very few metals possess them all, and many non-metallic elements possess several. The “alkali” metals are lighter than water; mercury is a fluid. The opacity of a mass is only in relation to its thickness, for Faraday beat out metals into plates so thin that they became transparent. All metals are not malleable, nor are they ductile. Tin and lead, for example, have very little ductility or tenacity, while bismuth and antimony have none at all. Carbon is a much better conductor of electricity than many metals in which such power is extremely varied. Lustre, again, though possessed by metals, is a characteristic of some non-metals. So we see that while we can easily say what is not a metal, we can scarcely define an actual metal, nor depend upon unvarying properties to guide us in our determination.

The affinity of metals for oxygen is in an inverse ratio to their specific gravity, as can be ascertained by experiment, when the heaviest metal will be the least ready to oxidise. Metals differ in other respects, and thus classification and division become easier. The fusibility of metals is of a very wide range, rising from a temperature below zero to the highest heat obtainable in the blow-pipe, and even then in the case of osmium there is a difficulty. While there can be no question that certain elements, iron, copper, gold, silver, etc., are metals proper, there are many which border upon the line of demarcation very closely, and as in the case of arsenic even occupy the debatable land.

Specific Gravity is the relation which the weight of substance bears to the weight of an equal volume of water, as already pointed out in Physics. The specific gravities of the metals vary very much, as will be seen from the table following—water being, as usual, taken as 1:—

Aluminium2·56Lead11·3Rubidium1·5
Antimony6·7Lithium·593Ruthenium11·4
Arsenic6·Magnesium1·74Silver105
Bismuth9·7Manganese8·Sodium·972
Cadmium8·6Mercury13·5Strontium2·5
Calcium1·5Molybdenum8·6Thallium11·8
Chromium6·8Nickel8·8Tin7·2
Cobalt8·9Osmium21·4Titanium5·3
Copper8·9Palladium11·8Tungsten17·6
Gold19·3Platinum21·5Uranium18·4
Indium7·3Potassium·865Zinc7·1
Iridium21·1Rhodium12·1Zircon4·3

Some metals are therefore lighter and some heavier than water.