15. To ascertain the chemical properties of minerals, one of the most important instruments is the blow-pipe. This is a tube which terminates in a cavity as fine as a small wire, and through which the air is forced, and made to play upon the flame of a candle. The flame is thus concentrated, and directed against small particles of the mineral to be examined, which is placed upon a bit of charcoal in a spoon of platina or silver. The air is forced into the blow-pipe by the mouth of the person using it, or by bellows attached to it for that purpose. Under this operation we have an opportunity of trying the action of other bodies upon minerals at a very high temperature; and the properties which these experiments bring into view enable us, in many cases, to ascertain, not only the nature, but even the component parts, of minerals.
SIMPLE MINERAL SUBSTANCES.
16. As a necessary introduction to the study of minerals, it is requisite to describe, in a brief manner, such simple substances as form their constituent parts. Few of these, it is true, are to be found in a separate, uncombined state; yet that they do exist, and that they are to be obtained from the minerals with which they are united, we have the proof of every day’s experience.
UNCONFINABLE FLUIDS.
17. There are some kinds of unconfinable fluids, the existence even of which is manifested only by their contact with other bodies, or becoming separated from them. They are of a nature too subtile to be collected or confined in our vessels for the purpose of examination, and the investigation of their properties has consequently been attended with peculiar difficulty. Those at present known are caloric, light, electricity, and magnetism; but of these the first only is immediately connected with the subjects of our present investigation.
18. Caloric.—Every one is acquainted with the different sensations of heat and cold. That matter which produces on our bodies the sensation of heat has the name of Caloric; heat being only an effect, of which caloric is the cause. This is extended in a greater or less degree through the whole extent of space, and penetrates into the interior of even the most solid bodies: in so doing it expands the particles of which they are composed, augments their bulk, and diminishes their solidity. The sun is the principal fountain from which the earth is supplied with this fluid; and it passes thence to us at the rate of 12,000,000 of miles per minute. The defect of caloric in any substance occasions the sensation called cold.
Were the world deprived of caloric, every species of organized being would, from that moment, cease to exist. It is the cause of all fluidity: to it every production of the earth has been most essentially indebted, even for its form and structure; and in no respect do the power and goodness of the Almighty appear more conspicuous than in the creation, dispersion, and continuance, of this most subtile and astonishing fluid.
19. All the various substances with which we are acquainted must be considered either as solid or fluid. Every substance is defined to be a solid in which the parts are so united or connected that it requires an external force to separate them. A fluid, on the contrary, is a body the parts of which are so loosely connected that they not only yield easily to any force impressed upon them, but also move freely amongst each other; and every fluid is a combination of caloric with some other substance.
20. Fluids are of two kinds: one of these, called liquids, have, when at rest, a smooth and distinct surface, and are distinguishable both by the sight and touch; the other, denominated gas, or gaseous fluids, have the appearance of air, and are not perceptible either to the sight or touch, except under certain circumstances. The latter are principally oxygen ([21]), azote or nitrogen, and hydrogen ([45]). We shall at present have occasion to speak only of the first.