[331] Professor Sonneschien, having submitted the so-called Gelseminic Acid to analysis thinks there can be no doubt that it is perfectly identical with æsculin, a glucoside obtained from the bark of the horse-chesnut—the Esculus hippocastanum.
Probably the alkaloid gelseminine may at some future time be introduced into medicine, since it would appear to be the chief ingredient to which the root owes its activity. It is strongly poisonous. Dr Wormley injected one eighth of a grain under the skin of a large cat, which in 40 minutes exhibited great prostration, and died in an hour and a half from the time of the injection of the poison. The properties of the gelseminic acid, the resin, the volatile oil, and other ingredients of the root, have not been fully investigated. See Tincture of gelsemium, GELSEMININE.
In the ‘American Journal of Pharmacy’ for April, 1877, Dr Wormley gives the following directions for the preparations of gelseminic acid, and gelsemine:—A given volume of fluid extract, acidulated with acetic acid, is slowly added with constant stirring to about eight volumes of water; after the separated resinous matter has completely deposited, the liquid is filtered, and the filtrate concentrated on a water bath, to something less than the volume of fluid extract employed. The gelseminic acid is then extracted from the concentrated fluid by ether, after which the liquid is treated with slight excess of carbonate of sodium, and the gelsemine extracted with ether or chloroform. For the extraction of the first of these principles, it is not essential that the liquid should be acidulated, but in the presence of a free acid the results are more satisfactory.
GEMS. Syn. Jewels; Gemmæ, L. “Gems are precious stones, which, by their colour, limpidity, lustre, brilliant polish, purity, and rarity, are sought after as objects of dress and decoration. They form the principal part of the crown jewels of kings, not only from their beauty, but because they are supposed to comprise the greatest value in the smallest bulk; for a diamond, no larger than a nut, or an acorn, may be the representative sign of the territorial value of a whole country, the equivalent in commercial exchange for a hundred fortunes, acquired by severe toils and privations.” “Among these beautiful minerals mankind have agreed in forming a select class, to which the title of gems or jewels has been appropriated; while the term precious stone is more particularly given to substances which often occur under a more considerable volume than fine stones ever do. Diamonds, sapphires, emeralds, rubies, topazes, hyacinths, and chrysoberyls, are reckoned the most valuable gems;—crystalline quartz, pellucid, opalescent, or of various hues, amethyst, lapis lazuli, malachite, jasper, agate, &c., are ranked in the much more numerous and inferior class of ornamental stones.” (Ure.)
Tests. The only tests applicable to gems and precious stones are the determination of their relative hardness and their specific gravity. By the first test, pastes or factitious gems are readily detected; but beyond this, owing to the difficulty of applying it, it ceases to be useful to persons unconnected with the trade. The determination of the specific gravity is, however, of more general application, as gems are generally dismounted when offered for sale, or are so set that they may be removed from their ‘mountings’ without injury or inconvenience. See Specific Gravity, and below.
Obs. The relative hardness of the different substances is measured by the power they possess of cutting or scratching the other substances having a smaller number attached to them in the table. Thus, no gem but the DIAMOND (20) will scratch either the RUBY (17) or the SAPPHIRE (16); and, for the same reason, a blue stone that will cut the EMERALD or the TOPAZ can be no other than the SAPPHIRE. The sp. gr. is ascertained in the usual manner, and will be found sufficiently indicative of the true nature of the stone when considered in connection with its other characteristics. The index of refraction is a certain key to the quality of the stone, in the hands of those who are capable of determining it, and may be applied to either mounted or unmounted gems. The most convenient instrument for the purpose is Wollaston’s ‘REFLECTING-GONIOMETER,’
Gems, Facti′′tious. These, with few exceptions, are made of very pure, fusible, highly transparent, and dense glass, usually termed ‘PASTE’ or ‘STRASS,’ which is generally formed of oxide of lead, potassa, and silica, with small quantities of other ingredients to increase the brilliancy and clearness. The characteristic tints are imparted by the addition of metallic oxides. The beauty of artificial stones and gems depends, chiefly, upon the tint of the real stones being exactly imitated, and upon proper care and skill being exercised in the cutting, polishing, and mounting them. All the coloured glasses, and enamels, may be worked up into artificial gems.
Table of the Hardness, Specific Gravity, and Refractive Power
of the principal Gems and Precious Stones, and some other
Minerals; compiled expressly for this work.
| Name. | Relative Hardness. | Specific Gravity. | Index of Reflection. |
| Agate | 12 | 2·6 | |
| Amethyst (occidental) | 11 | 2·7 | |
| Calcareous spar | 6 | 2·7 | |
| Chalk | 3 | 2·7 | |
| Chrysolite | 10 | 3·7 | |
| Cornelian | 11 | 2·7 | |
| Crystal | 11 | 2·6 | |
| Diamond (bluish) | 19 | 3·3 | 2·439 |
| Diamond (cubic) | 18 | 3·2 | |
| Diamond (from Ormus) | 20 | 3·7 | |
| Diamond (pink) | 19 | 3·4 | |
| Diamond (yellowish) | 19 | 3·3 | |
| Diamond (average colourless) | 19 to 20 | 3·3 to 3·55 | |
| Emerald | 12 | 2·8 | |
| Fluor spar | 7 | 3·5 | 1·434 |
| Garnet | 12 | 4·4 | 1·815 |
| Glass | various | 2·3 to 3·62 | 1·525 to 2·028 |
| Glass (crystal or flint) | 3·0 to 3·6 | 1·830 to 2·028 | |
| Glass (plate) | 2·5 to 2·6 | 1·514 to 1·542 | |
| Gypsum | 5 | 2·3 | |
| Jasper (green) | 11 | 2·7 | |
| Jasper (reddish yellow) | 9 | 2·6 | |
| Onyx | 12 | 2·6 | |
| Opal | 10 | 2·6 | |
| Quartz | 10 | 2·7 | 1·548 |
| Ruby | 17 | 4·2 | 1·779 |
| Ruby (pale, from Brazil) | 17 | 3·5 | |
| Ruby (spinelle) | 13 | 3·4 | 1·764 |
| Sapphire (deep blue) | 16 | 3·8 | 1·794 |
| Sapphire (paler) | 17 | 3·8 | |
| Sardonyx | 12 | 2·6 | |
| Schoerl | 10 | 3·6 | |
| Topaz | 15 | 4·2 | |
| Topaz (Bohemian) | 11 | 2·8 | |
| Topaz (whitish) | 14 | 3·5 | |
| Tourmaline | 10 | 3·0 | |
| Zeolite | 8 | 2·1 | |
| Zircon | — | — | 1·961 |
MM. Fremy and Feil have lately succeeded