THE PHILOSOPHY

OF

EXPERIMENTAL CHEMISTRY.

PART XV.

OF METALS.

I. The metals are distinguished by certain obvious and physical properties; as,

1. Lustre. The brilliancy which the metals possess, is known by the name of metallic lustre. This property is occasioned by their reflecting much more light than any other bodies, which seems to depend on the closeness of their texture.

2. Opacity. Metals are perfectly opaque, or impervious to light. Newton observed, that gold leaf 2000 of an inch thick, when held between the eye and the light appears of a lively green, and, according to him, transmits the green coloured rays. Silver leaf, however, Tooooo of an inch thick, is completely impervious to light. Metals are therefore considered opaque.

3. Fusibility. That metals may be melted by the application of heat, is a well known property. They still retain their opacity. The metals, however, differ

B

in their fusibility. Thus, mercury remains fluid in the common temperature of the atmosphere, and even requires intense cold to make it solid; while other metals, as platinum, cannot be melted except by the most violent heat.

4. Weight. The specific gravity of the metals is exceedingly various. The greater number of them are heavier than any other known substances.

Several of the new metals, discovered by Mr. Davy, are not so heavy as water. Thus plantinum is 23 times heavier than water, whilst the specific gravity of potassium is only 0.6, that of water being 1.

5. They are all conductors of electricity.

6. They possess different degrees of hardness; and the ingenuity of the artist has rendered some of them considerably hard by artificial means. Hence the numerous instruments made of steel.

7. Elasticity. This property depends upon the hardness of the metal, and may be increased by the same process by which their hardness is increased.

8. Malleability. The capacity of being extended and flattened when struck with a hammer, is called malleability. This is a useful property of the metals. All metals do not possess it in the same degree. Heat increases it remarkably.

9. Ductility. The capacity of being drawn out into wire, by means of a certain contrivance, is called ductility. This property is also wanting in some of the metals.

10. Tenacity. Tenacity is the power which a metallic wire, of a given diameter, has of resisting, without breaking, the action of a weight suspended from its extremity. Ductility depends, in some measure, on this property. The metals differ in this capacity. An iron wire, for instance, th of an inch in diameter, will support a weight of 500 pounds. A lead wire, on the contrary, of the same diameter, will not support above 29lbs.

II. The metals at present known, including those discovered by Mr. Davy, amount to 40. Twelve of these are imperfectly known, and some philosophers

have expressed their doubts of their existence. As these metals have been obtained from the alkalies and earths, we have noticed them when treating of these substances. We have to consider, therefore, the remaining metals, which are 28 in number. Seven of these were known to the ancients, and seventeen have been discovered since the year 1730. In the arrangement of the metals, Thomson has adopted the following, in four classes, each of which is characterised by some general property.

Those of the first class, by way of eminence, were formerly considered perfect metals, and all the

rest

were called semi-metals or imperfect metals. But this distinction is disused.

The metals as they are found, are generally mineralized, by the union of sulphur, oxygen, &c. forming ores. The ores of metals have been classified or arranged in several ways.

The following arrangement of ores, is adopted by professor Cooper.*