Page:Popular Science Monthly Volume 17.djvu/274

262 dissolves in a gaseous solvent, from which solution of carbon crystals are then obtained, just as table-salt is produced by the evaporation of brine, and these crystals are diamond.

The temperature at which the dissociation of the hydrocarbon is effected must be very high, and the pressure enormous, so that the great difficulty of the process lies in the construction of an inclosing vessel strong enough to withstand the combination of heat and disruptive force. Coiled tubes of wrought iron, of half an inch bore and four inches external diameter, have been torn open in nine cases out of ten.

The mineralogical tests which demonstrate the genuineness of diamond are as follows: It must scratch topaz and sapphire, its angles must be those of a regular octahedron, it must burn without leaving any residue, and it must exert little or no action on polarized light. Professor Maskelyne, of the British Museum, has already stated in the "Times" that Mr. Hannay's crystals satisfy all these tests. They score topaz and sapphire easily and deeply; the angle of their cleavage-faces, which could not be measured with great accuracy on account of the minuteness of the gems, is 70° 29', while that of the diamond is 70° 30'. Particles ignited on platinum glow and disappear exactly as the gem would do, and they are very nearly inert in polarized light.

It is not long since science rejected the claims of another Glasgow investigator to the artificial production of crystalline carbon, and it is somewhat singular that Mr. Hannay's successful solution of this great chemical problem should have followed so quickly upon Mr. McTear's failure.

That the diamonds in this case are real there is now no question; and it is quite possible that, just as experience has taught chemists how to produce large and perfect crystals from solutions which under ordinary treatment yield only small and imperfect specimens, so Mr. Hannay may by and by succeed in making diamonds as big as the Koh-i-noor or the Regent.

We learn, however, from the investigator's own statement, that up to the present time it has cost him five pounds to produce five shillings' worth of diamond; but, even if the world of fashion is destined to deplore the degradation of its cherished gem, we may be sure that, long after some new toy has satisfied society for its loss, the crystallization of carbon will possess for the greater world of science the same kind of interest as clings around the discovery of oxygen by Priestley, or the demonstration of magneto-electricity by Michael Faraday.—Belgravia.