Composition of Diamonds

The early experiments conducted with diamonds to explain strange properties of diamonds and to discover the composition of the diamond

The ancients had no suspicion of the true nature of the diamond. To have any idea of this subject, it was necessary that the bases of modern chemistry should be established, or at least that the complex phenomenon of combustion should have received its true explanation. Newton suspected from its wonderful refractive power that the diamond was combustible, but even as late as the middle of the eighteenth century, the definition of its composition, given in a standard work on physics, was--"the purest and finest earth, the most ethereal fire, and the most limpid water."

The first important fact relative to the nature of the diamond was established by Boyle about the middle of the seventeenth century. He showed that under the influence of a great heat the diamond disappeared. A little later, in 1694, Cosmo III., Grand-duke of Tuscany, had a diamond subjected at Florence to the intense heat of the sun's rays, by aid of a concave mirror. The experiment was conducted by Averini, preceptor of the Prince John Gaston, son of Cosmo, and Targioni, member of the Academy del Cimento. The diamond first split, then emitted sparks, and finally disappeared.

This experiment was repeated at Vienna by Francis Stephen of Lorraine, afterwards Francis I. of Austria. The sun's rays were replaced by the fire of a furnace, with the same result. Nearly a hundred years after the experiment at Florence it was renewed in Paris by D'Arcet, Rouelle, and Macquer. On the 26th of July, 1771, these savants burned in the laboratory of Macquer a beautiful diamond furnished by an amateur, Godfrey de Villetaneuse. That the diamond had disappeared was certain, but the question arose whether it had actually burned or was merely volatilized.

In the midst of the discussion, Le Blanc, a celebrated jeweller of the day, ignoring the experiments carried out at Florence, Vienna, and Paris, affirmed that fire had no effect upon the diamond. He had frequently, he said, submitted diamonds to a high temperature to remove certain defects, and the heat had never in the least degree deteriorated the stone.

To prove his assertion he tried an experiment before a great number of spectators in the laboratory of Rouelle. He enveloped a diamond in a mixture of lime and charcoal dust, introduced it into a crucible, and exposed it to a violent heat. After about three hours the interior of the crucible was examined, and nothing was found there but the little box that the diamond had occupied. The experiment had resulted like the others, and Le Blanc retired amid the acclamations of his opponents, "without his diamond, but still unconvinced."

Light had now begun to dawn upon the question, but it was still far from being settled. Accordingly Cadet, Macquer, and the illustrious Lavoisier made preparations for new experiments on the subject, when a skilful lapidary named Maillard presented himself before them, and maintained, as Le Blanc had done, that fire had no effect on the diamond. He offered to submit three diamonds to the most prolonged and intense heat, but he stipulated that he should be allowed to carry out the experiment in his own way.

This being granted, Maillard took the bowl of a tobacco-pipe, placed the three diamonds in it in the midst of charcoal powder closely packed, closed the mouth of the pipe with a cover of iron, and then shut up the whole in a crucible filled with chalk and covered with a siliceous coating. (See Fig. 30.) The crucible was now subjected to a temperature such that at the end of four hours it was completely soft and on the point of melting, when the fire was slackened. After the crucible had been allowed to cool it was carefully broken open, the pipe-bowl was found to be entire, with the charcoal in it as black as at first; and in the midst of this the three diamonds, in every respect unaltered and uninjured.

Some diamonds prepared by Maillard, and submitted for twenty-four hours to the enormous temperature of a porcelain furnace, resisted the heat like the preceding.

Analogous experiments were made in different parts of Europe, sometimes with the one, sometimes with the other of the preceding results. The facts remained inexplicable till--on the principal phenomena of combustion being established--it was noticed that the diamond had always disappeared when it had been heated in the presence of air, while it had undergone no modification when removed from the action of the air by means of substances such as powdered charcoal, lime, &c.

Arrived at this stage, the question could not long remain unsolved; and the solution was soon furnished by two of the creators of the science of chemistry--Humphry Davy in England, and Lavoisier in France.

"And what is the diamond?" asks Babinet, who has such a quick eye to the poetry of science. "The most precious thing in the whole world. And what is carbon? The most common material that is known; one that not only exists in vast quantities in the bowels of the earth, but that plants and trees of every kind contain, in an inconceivable quantity. Silver can hardly pay for the diamond; for if we imagine a diamond of the weight of a twenty-five franc piece, it would weigh about 125 carats, and cost at least four millions of francs; while an equal weight of carbon, even having recourse to the smallest copper pieces, would have no appreciable value. And yet the diamond and carbon are identical. Diamond is crystallized carbon."

Everyone knows the pungent gas that escapes from fermented liquors--cider, beer, wine, &c.--and is introduced artificially into aerated waters. It is formed by the combination of carbon with one of the elements of the air (oxygen), and is called by chemists carbonic acid. This substance is produced whenever carbon, or substances which contain carbon, are burned in contact with the air; and not the slightest trace of it is ever found, if the substance burned does not contain carbon.

After this grand fact had been established, it was very easy to find out if the diamond contained carbon, and also whether this was its sole constituent. To settle the first question, the celebrated Lavoisier had recourse to the experiment represented by Fig. 31.

A bell-glass filled with oxygen was reversed in a basin containing mercury. A cupel placed at the extremity of a little column received the diamond, upon which the sun's rays were concentrated by means of a burning-glass.

The diamond disappeared; and it was proved that the glass, which at the commencement of the experiment had contained no trace of carbonic acid, contained a great quantity after the disappearance of the diamond. The diamond then contained carbon as one of its elements. Davy did not remain satisfied with this.

By analogous experiments he showed that the combustion of the diamond in oxygen produced carbonic acid only; the diamond, then, must be composed of carbon and nothing else.

Certain doubts still lingered upon this point, but they were dispelled by the publication in 1841 of the grand work of MM. Dumas and Stass upon the equivalent of carbon.

In their experiments these two savants burned a great number of diamonds, but they corrected an error the maintenance of which would have been a veritable calamity to science. The capital importance of the results obtained by MM. Dumas and Stass completely justified the use of such exceptional fuel.

It is very probable that the absolutely pure diamond consists exclusively of carbon; but perfectly pure diamonds are very rare. All those burned by MM. Dumas and Stass left a residuum or ash, if we may call it so, sometimes in the form of a spongy network of a reddish-yellow colour, sometimes as crystalline particles of a straw-yellow colour, sometimes as colourless and crystalline fragments. This residuum varied from 1/500 to 1/2000 of the weight of the diamond employed.

It used to be believed that the diamond could be consumed only with great difficulty. This error is corrected by one of the most fascinating experiments of chemistry. It was first performed by M. Morren, senior of the faculty of sciences at Marseilles.

He took a wire of platinum, and by means of a little cone of wood gave it the shape represented by Fig. 32.

He then fixed the upper end of the wire in a cork, and placed in the little receptacle the diamond to be burned. A phial filled with oxygen was at hand. By aid of a blowpipe the temperature of the diamond and its support was elevated to white heat, and then was plunged quickly into the phial of oxygen (Fig. 33). The diamond immediately kindled, and continued to burn with a steady glow infinitely more vivid than that which could have been obtained from any other variety of carbon.

M. Morren has also proved that the diamond burns in layers: for if the combustion is arrested at any period, the special system of crystallization is still regularly displayed.

This is a very important point, since it excludes all idea of fusion for the diamond.

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