solution as thick as molasses of silicate of soda, which brings about a slow separation of the silicic acid. When, in so doing, he used a solution of the sulphate of nickel protoxide, he obtained apple-green stones, such as the chrysoprase. Thus we see that, as long as the process of separation lasts, we may talk of the growth of precious stones; and we perceive, from the laws of crystallization, how by the attraction of similar parts, and the exclusion of foreign ones, the formation of precious stones of perfectly "pure water" among the more impure ones, which are frequently found, becomes more intelligible.
Another process of crystallization is the slow cooling of molten substances. This can be explained very strikingly to students of chemistry if a kettle of sulphur or molten bismuth is cooled slowly, until it is covered with a crust of congealed matter, so to speak. Pierce that crust in the middle, and pour out a portion of the liquid, and there will form on the walls of the cavity thus created crystals of surpassing beauty, and the whole assumes the appearance of a so-called crystal druse, a form often assumed by amethysts and other half-precious stones. It has been thought that, to make artificial diamonds, it was necessary only to melt coal; but, unfortunately, the results thus far obtained are of no value.
Nature's most successful way of producing precious stones was not to dissolve minerals, but to put them into a fiery liquid condition, and to separate the new productions slowly from their former impure parts by chemical and electric influences, as we shall see directly. The earth, like the sun and most fixed stars at present, was undoubtedly formerly in a fiery, liquid condition. Then the elements were commingled; all substances met, and entered the strangest combinations; the whole globe was an immense chemical laboratory. The earthy substances with the light metals, at the last period of those gigantic processes, probably formed the "mother-liquor," from which, under various chemical agencies, there separated now valuable metals, now grains of gold, and still more frequently substances which were ennobled by crystallization. The "mother-liquor," cooled with its productions, we call primitive formations—granite, feldspar, porphyry, etc. It may here be stated that these primitive processes have recently been imitated in part, and that two principal components of feldspar, albite and orthoclase, have lately been obtained from a fiery, liquid mixture of minerals.
Precious stones so formed would be colorless if, in the terrible furnace of the primordial world, fire-proof metals had not taken upon themselves the task performed by aniline in our present dying-works. Long before there were colored plants and animals, metals played the part of pigments in Nature, and thus produced, in stones, colors almost surpassing in brilliancy those to be found in the animal kingdom. Rubies and emeralds are probably colored with chrome, sapphires with cobalt, lapis-lazulis with iron, and other precious stones with copper, nickel, manganese, etc. But we only have to refer our readers to the