All stones formed by nature are compounded, and to distinguish them from one another, and ascertain the parts of which they consist, is the subject of lithology, a very extensive branch of knowledge.
All the simple earths are nearly, if not absolutely, infusible; but when they are mixed they may all be fused.
LECTURE XXI.
Of Ores.
Metallizable earths, commonly called ores, when united to phlogiston, make the metals, distinguishable for their specific gravity, their opacity, shining appearance, and fusibility.
All the proper metals are malleable, and those which are not so are called semi-metals.
The metals again are subdivided into the perfect and imperfect. The former, which are gold, silver, and platina, suffer no change by fusion, or the longest continued heat: whereas heat calcines or dissipates the phlogiston of the imperfect metals, which are mercury, lead, copper, iron, and tin, so that they return to the state of earth; and this earth is always heavier than the metal, though of less specific gravity, having received an addition of weight from water or air: but these earths, or ores, being exposed to heat in contact with substances containing phlogiston, again become metals, and are then said to be revived.
The semi-metals are bismuth, zinc, nickel, regulus of arsenic, of cobalt, of antimony, of manganese, of wolfram, and of molybdena.
All metallic substances are crystallizable, and each in a peculiar form, which is discovered by leaving a hole in the bottom of the crucible in which they are melted, and drawing out the stopper, when the mass is beginning to lose its fluidity.