At the end of thirty-six hours the current is cut off, and the furnace is allowed to cool, the workmen pulling down the brick as rapidly as they dare. At the centre of the furnace, surrounding the core, there remains a solid mass of carborundum as large in diameter as a hogshead. Portions of this mass are sometimes found to be composed of pure, beautifully crystalline graphite. This in itself is a surprising and significant product, and it has opened the way directly to graphite-making on a large scale. An important and interesting feature of the new graphite industry is the utilisation it has effected of a product from the coke regions of Pennsylvania which was formerly absolute waste. To return to carborundum: when the furnace has been cooled and the walls torn away, the core of carborundum is broken open, and the beautiful purple and blue crystals are laid bare, still hot. The sand and the coke have united in a compound nearly as hard as the diamond and even more indestructible, being less inflammable and wholly indissoluble in even the strongest acids. After being taken out, the crystals are crushed to powder and combined in various forms convenient for the various uses for which it is designed. I asked Mr. Acheson if he could make diamonds in his furnaces. "Possibly," he answered, "with certain modifications." Diamonds, as he explained, are formed by great heat and great pressure. The great heat is now easily obtained, but science has not yet learned nature's secret of great pressure. Moissan's method of making diamonds is to dissolve coke dust in molten iron, using a carbon crucible into which the electrodes are inserted. When the whole mass is fluid, the crucible and its contents are suddenly dashed into cold water or melted lead. This instantaneous cooling of the iron produces enormous pressure, so that the carbon is crystallised in the form of diamond. But whatever it may or may not yet be able to do in the matter of diamond-making, there can be no doubt that the possibilities of the electrical furnace are beyond all present conjecture. With American inventors busy in its further development, and with electricity as cheap as the mighty power of Niagara can make it, there is no telling what new and wonderful products, now perhaps wholly unthought-of by the human race, it may become possible to manufacture, and manufacture cheaply. CHAPTER V HARNESSING THE SUN _The Solar Motor_ It seems daring and wonderful enough, the idea of setting the sun itself to the heavy work of men, producing the power which will help to turn the wheels of this age of machinery.