Page:Popular Science Monthly Volume 17.djvu/273

Rh of things then so obscure as to be thought hopeless, by dissolving in the liquid under examination some solid substance which fused at a temperature much above the critical point of the fluid.

Sulphur, for example, melts at 111° Fahr., and is soluble in carbon dioxide, a liquid whose boiling-point is 42°. When such a solution was vaporized it was found that the sulphur was not deposited, but remained diffused in the atmosphere of dioxide vapor; or, in other words, the sulphur was dissolved in the gas. If the side of a tube containing such a gaseous solution of sulphur is approached by a red-hot iron, the part next the source of heat becomes coated with a crystalline deposit, which redissolves into the gas on the removal of the heat. In the course of his experiments on the solubility of solids in gases Mr. Hannay further noticed that many bodies, such as alumina and silica, which, like carbon, are insoluble in water, dissolved to a considerable extent in "water-gas," or water at the critical point when it is neither a true liquid nor a true gas. This fact suggested to him that a solvent might even be found for the hitherto insoluble element, carbon; and, as gaseous solutions were found to yield crystalline solids in almost every case upon the withdrawal or dilution of the solvent gas, it was hoped that, from such a gaseous solution of carbon, crystals of diamond might be obtained.

After a large number of experiments, however, it was found that neither charcoal, lampblack, nor black-lead would dissolve in the most probable solvents when these were brought to their critical points, and a new road out of the difficulty had accordingly to be sought.

Chemists have long known that what is called the "nascent" state of matter is one very favorable to chemical combination. Thus nitrogen, for example, refuses to combine with hydrogen, but, if these two substances are simultaneously liberated from some previous combination, they unite at the moment of birth with the utmost ease. Bearing this in mind, it was ascertained that, when a gas containing both carbon and hydrogen is heated under pressure in presence of a metal, the hydrogen is attracted by the metal and the carbon left free.

Mr. Hannay attacked this nascent carbon with many gaseous solvents, and it is his triumph to have found what he sought. In doing so, he has removed a reproach of long standing from the science of chemistry; for, whereas the larger part of that science is occupied with the chemistry of carbon and its compounds, this element has never previously been either dissolved or vaporized by man.

What the solvent is, we are not at present definitely told; we only know that it is some nitrogen compound, probably a cyanide; but the process is quite intelligible in the absence of this information, while its products are open to the examination of experts.

A hydrocarbon vapor, such as petroleum, is decomposed at a high temperature and under great pressure. As the hydrogen and carbon part company, the former is absorbed, while the latter, being nascent,