Calcite (Carbonate of Lime).—Flame glows very strongly; infusible; effervesces freely in cold hydrochloric acid.
Dolomite.—Flame, with hydrochloric acid, like calcite; infusible; effervesces in hot hydrochloric acid.
Magnesite.—Infusible; with cobalt nitrate a fair magnesia reaction on charcoal, i.e., turns into a dull pink; effervesces in hot hydrochloric acid.
Manganese.—With borax in oxidising flame a red-violet bead is obtained, but with the reducing flame it is colourless.
The above are commonly met with in brick-earths; for other minerals and substances also found, the reader may be referred to special works dealing with blowpipe analysis.
CHAPTER VIII.
THE CHEMISTRY OF BRICK-EARTHS (Continued).
In this chapter we shall fulfil our promise (ante p. 58) to explain in an elementary manner the precise meaning of ordinary commercial chemical analyses of some typical earths used in brickmaking, etc. We may commence by explaining a few terms used by the chemist.
An atom is the smallest imaginable portion of matter, and all matter is said to consist of atoms. A molecule is the smallest conceivable combination of atoms, and every compound substance is ultimately built up of molecules. An element is a substance that has hitherto defied the efforts of the chemist to subdivide or split up. Over seventy of these elementary substances are at present known, and their number is being constantly added to. Again, by improvement in analytical methods, a so-called element may be subdivided, and thus removed from the list. The elements are classified into metals and non-metals; and it is convenient to give each of them a symbol to save trouble in writing, and to render clearer to the reader the chemical nature of a compound body. Thus, the symbol for the element aluminium is Al; for silicon Si; for carbon C; for calcium Ca; for oxygen O; for iron Fe; for hydrogen H; for chlorine Cl; and so on.
We are taught by chemistry that elements are capable of combining only in definite proportions, and that each substance possesses a definite proportion peculiar to itself. That proportion is called the atomic weight of the element; or, it is the relative weight of the atom of each substance compared with that of the lightest substance known, hydrogen.