Second Method of Artificial Production of Precious Stones

In the year 1823 M. Becquerel, one of the most eminent of French physicists, formed the idea of using the currents of the voltaic pile to determine combinations, and not merely decompositions.

Instead of employing powerful currents, such as were used to produce decomposition, he applied to his purpose very feeble currents, and the results obtained surpassed his expectations.

The simple apparatus which he used is shown in Fig. 90. It is a tube curved in the form of the letter U. The curved part is filled with clay, to prevent the liquids contained in the branches from flowing together, without interfering with the production of molecular actions and transports. The two liquids are, moreover, placed in direct communication by means of a metallic wire.

One of the substances reproduced by M. Becquerel was the sulphide of silver crystallized.

In the left branch of his tube he placed a saturated solution of nitrate of silver, in the right branch a solution of sulphide of potassium, and established a communication between the two liquids by the aid of a silver wire. Silver was deposited on the left-hand wire, and crystals of the double sulphide of silver and potassium on the right; but the sulphide of potassium being rapidly destroyed by the nitric acid, there remained on the wires in the clay, and on the walls of the tube, perfectly defined crystals of sulphide of silver, presenting all the characteristics of natural crystals. As the current was very weak, the crystals took long to form; some of them from seven to eight years.

The method by direct fusion could only be expected to produce fusible minerals. The electric method had given neither a silicate nor an aluminate; and, as crystallized bodies belonging to these classes are by far the most important, Ebelman set himself to solve the problem of their production.

Every one knows that if crystalline substances--such as salt, for instance--are dissolved in water, and the solution is allowed to stand in the open air, the water will disappear after a time, and the substance that was dissolved in it will be left in the shape of solid crystals.

Reasoning by analogy, then, Ebelman came to the conclusion that he must find some body capable of dissolving infusible combinations without contracting combinations with them, and capable of being reduced to vapour at a still higher temperature.

Experiment taught him that boric acid possessed the requisite properties in a high degree.

Being director of the manufactory of porcelain at Sevres, he profited by the high temperatures developed in the furnaces to make some very interesting experiments, which were afterwards produced with still greater success at the continuous fires of furnaces placed at M. Ebelman's disposal by M. Bapterosses, fabricator of buttons of ceramic paste.

Mixtures in proportions corresponding to the composition of the stones to be produced were placed in capsules of platina along with boric acid, and the whole was submitted to a high temperature. The boric acid first melted, and afterwards volatilized, and, as Ebelman had anticipated, the substances that it held in solution crystallized.

In this way he produced the spinel ruby so perfectly that it could not be distinguished by Dufrenoy from the natural stone. This was effected by subjecting a compound consisting of proper proportions of alumina, magnesia, the green oxide of chromium and boric acid to a high temperature in the muffle of a furnace for eight days. He obtained crystals measuring 0.197 inch on a side.

The method employed by M. Senarmont is the method of dissolution by means of water. It is, without doubt, the method employed by nature in caverns and calcareous crevasses, where, after a number of years, often very small stalactites of crystallized carbonate of lime are produced. These productions, and the phenomena of thermal springs, where the pressure and heat are often very high, and the deposits of mineral waters, suggested to M. de Senarmont the method of his experiments.

He introduced into the most resisting sort of glass tubes the elements of the substances he wished to produce. He placed together gelatinous silica, and a body susceptible of furnishing carbonic acid by the action of heat (bicarbonate of soda), and having closed the tubes at the lamp, submitted them to variable temperatures and variable pressure.