in manufacturing artificial corundum, ruby and topaz, having a composition the same as the natural stones. The process by which they have effected this consists in fusing together at a red heat, in the furnace of a glass works for a considerable time, a fusible aluminate (such as aluminate of lead), and some silicious body.
The silica is found to unite with the lead, and to liberate the alumina in the crystalline form. When equal weights of alumina and red lead are heated together in a crucible made of some refractory silicious substance, the above conditions if the temperature has been maintained sufficiently long and high ensue, and there is found in the crucible at the end of the operation a layer of silicate of lead, and very frequently another of pure crystallised alumina or corundum.
The ruby colour is given by adding to the mixture in the crucible two or three per-cent. of bichromate of potash, the blue being produced by the addition of a small quantity of oxide of cobalt, with a trace only of bichromate of potash. A film of silicate of lead very frequently adheres to the ruby crystals, and this has to be removed.
In some instances, however, the crystals occur nearly pure, and are precisely similar to the natural gems in crystalline form, composition, hardness, and lustre.
Upon being heated, the artificial ruby, like the natural one, loses its rose colour, and recovers it again on cooling. It is said that the factitious gems hitherto obtained are not, as a rule, equal in lustre to the natural ones, and are consequently not so well suited for jewellers’ work; also that they do not present to
the lapidary conditions favorable to cleavage or cutting. They are, however, very well adapted for the works of watches. See Enamels, Pastes, &c.
GENE′VA. See Gin and Hollands.
GEN′TIAN ROOT. Syn. Gentinæ Radix, L. The dried root of Gentiana lutea, or ‘yellow gentian.’ Dose, 10 to 30 gr.; as a simple bitter tonic, and stomachic, in dyspepsia, loss of appetite, gout, &c. It was formerly a favourite remedy in agues. “Joined with galls or tormentil, and given in sufficient quantity, it has not failed in any intermittents in which I have tried it.” (Dr Cullen.) In excessive doses it is apt to relax the bowels and disturb the system. When taken for some time, it imparts its bitter flavour to the perspiration and urine. See Decoction, Extract, &c.
GEN′TIANIN. Syn. Gentianine; Gentianina, L. A substance obtained by MM. Henry and Caventou from the root of common gentian.
Prep. 1. Gentian root (in powder) is digested for 2 or 3 days in cold ether, with agitation, and the filtered tincture evaporated to dryness; the residuum is dissolved in rectified spirit, and the solution is again evaporated; the semi-crystalline mass is, lastly, redissolved in either alcohol or ether, and crystallised by careful evaporation.