The Boron Diamond

Before we give an account of the attempts that have been made to produce the diamond by artificial means, it is necessary to state a few facts regarding two other simple bodies whose properties very closely resemble those of carbon, and which have an important bearing on the subject of which we are about to speak. These bodies are boron and silicon.

Not only do these bodies present exactly the three modifications presented by carbon-that is to say, they are either crystallized, graphitoid, or amorphous-but the crystallized boron so closely corresponds to the real diamond that it has been named from analogy the boron diamond.

Crystals of boron are limpid and transparent; sometimes coloured garnet-red, and sometimes honey-yellow, by the presence of foreign matters. Their refrangibility can only be compared to that of the diamond, and they present the same effects of reflected and refracted light. They possess the quality of hardness, too, in such a degree as to scratch the oriental ruby and corundum; and M. Froment has used a crystal of boron to scratch the surface of a diamond.

The cutting of the diamond with powder of boron was attempted by M. Voorzanger, of Amsterdam, with entire success; only that a larger quantity was used than would have been necessary of diamonddust, and the work was accomplished more slowly.

The same success attended the cutting of an exceedingly hard diamond in the collection of the Normal School at Paris. Its angular edges, and a furrow which marred it, were removed by a wheel covered with powder of boron. M. Guillot, who directed the experiment, confirmed the observation of M. Voorzanger concerning the superlative qualifications of boron-dust for cutting and polishing diamonds.

It has been further observed that the greater number of the powerful agents at the disposal of modern chemistry are without action upon boron. "It is," says M. Malaguti, "the most unalterable of simple bodies; and if the day comes when it can be obtained in large crystals, it may replace the diamond."

Boron is extracted from boric acid, a production elaborated by nature in the depths of the earth, and whose appearance at the surface is one of the curiosities of natural chemistry.

In certain volcanic districts of Tuscany jets of hot steam, mixed with carbonic acid, nitrogen, hydrochloric acid, &c., and also a small quantity of boric acid, issue from openings in the soil called soffioni or fumarolles. Round these soffioni circular basins of various diameters are constructed, into which the water of neighbouring springs is conducted. The gaseous jets, forcing their way through the water, impregnate it with the boric acid, the quantity held in solution being increased by letting the water flow through a series of basins, in each of which it receives an additional supply of the acid. When it is sufficiently charged with the acid it is admitted into the final reservoir, where it is allowed to stand for a time and deposit its earthy particles. The clear solution is now run off, concentrated in boilers by the heat of the jets themselves, and the acid obtained by evaporation.

The manner in which MM. Deville and Voehler obtained crystallized boron, once so difficult to obtain, is as follows:--

Into a charcoal crucible 80 grammes of aluminium is introduced in large morsels, and 100 grammes of boric acid reduced to fragments. This crucible is placed with charcoal paste in a crucible of plumbago, and the whole is subjected to the action of heat in a furnace producing a heat capable of easily melting pure nickel. This temperature is kept up for five hours; and when, after the cooling, the crucible is broken open, it is found to contain two distinct layers. The lower layer is vitreous, and formed of boric acid and alumina; the other is metallic, gray, and cavernulous, and is roughened and impregnated throughout its whole mass with little crystals: this is crystallized boron.

The mass in which these crystals are distributed is formed principally of aluminium, but it contains also variable quantities of iron and of silicon.

The whole is boiled in a lixivium of soda, of medium concentration, when the aluminium dissolves. That which remains is boiled with hydrochloric acid, and the iron is thus removed. The part not yet attacked is treated by a mixture of hydrofluoric acid and nitric acid, which removes the last traces of silicon. The boron, which has not experienced the slightest action under the influence of the preceding agents, remains as the definitive residue.

The boron thus obtained, however, is not perfectly pure; its analysis by M. Deville gives the following results:--

Boron,.......... 89.1

Aluminium,....... 6.7

Carbon,.......... 4.2

100.0

It is very remarkable that this proportion of carbon (more than 4 to 100) does not prevent the boron from being transparent; and what is still more extraordinary is, that the boron becomes more and more transparent as the proportion of carbon increases.

M. Deville's conclusion is therefore inevitable, viz. that it is nearly certain that the carbon contained in the crystallized boron is present there in the state of diamond.

We perceive, then, that boron is worthy of the utmost attention, as being capable of affording a special diamond, and for its possible concurrence in the artificial production of real diamonds.