He recognised that in all diamonds which he had consumed—­and he consumed some L150 worth in order to assure himself of the fact—­there were always traces of iron in their composition.  He saw that iron in fusion, like other metals, always dissolves a certain quantity of carbon.  Might it not be that molten iron, cooling in the presence of carbon, deep in volcanic depths where there was little scope for the iron to expand in assuming the solid form, would exert such tremendous pressure upon the particles of carbon which it absorbed, that these would assume the crystalline state?

He packed a cylinder of soft iron with the carbon of sugar, and placed the whole in a crucible filled with molten iron, which was raised to a temperature of 3000 deg. by means of an electric furnace.  The soft cylinder melted, and dissolved a large portion of the carbon.  The crucible was thrown into water, and a mass of solid iron was formed.  It was allowed further to cool in the open air, but the expansion which the iron would have undergone on cooling, was checked by the crucible which contained it.  The result was a tremendous pressure, during which the carbon, which was still dissolved, was crystallised into minute diamonds.

These showed themselves as minute points which were easily separable from the mass by the action of acids.  Thus the wonderful transformation from sugar to the diamond was accomplished.

It should be mentioned that iron, silver, and water, alone possess the peculiar property of expanding when passing from the liquid to the solid state.

The diamonds so obtained were of both kinds.  The particles of white diamond resembled in every respect the true brilliant.  But there was also an appreciable quantity of the variety known as the “black diamond.”  These diamonds seem to approximate more closely to carbon as we are most familiar with it.  They are not considered as of such value as the transparent form, but they are still of considerable commercial value.  The carbonado, as this kind is called, possesses so great a degree of hardness that by means of it it is possible to bore through the hardest rocks.  The diamond drill, used for boring purposes, is furnished around the outer edge of the cylinder of the “boring bit,” as it is called, with perhaps a dozen black diamonds, together with another row of Brazilian diamonds on the inside.  By the rotation of the boring tool the sharp edges of the diamonds cut their way through rocks of all degrees of hardness, leaving a core of the rock cut through, in the centre of the cylindrical drill.  It is found that the durability of the natural edge of the diamond is far greater than that of the edge caused by artificial cutting and trimming.  The cutting of a pane of glass by means of a ring set with an artificially-cut diamond, cannot therefore be done without injuring to a slight extent the edge of the stone.