§ 4 Combustion of a Diamond by Radiant Heat
The experiment of burning a diamond in oxygen by the concentrated rays of the sun was repeated at Florence, in presence of Sir Humphry Davy, on Tuesday, the 27th of March, 1814. It is thus described by Faraday:—‘To-day we made the grand experiment of burning the diamond, and certainly the phenomena presented were extremely beautiful and interesting. A glass globe containing about 22 cubical inches was exhausted of air, and filled with pure oxygen. The diamond was supported in the centre of this globe. The Duke’s burning-glass was the instrument used to apply heat to the diamond. It consists of two double convex lenses, distant from each other about 3½ feet; the large lens is about 14 or 15 inches in diameter, the smaller one about 3 inches in diameter. By means of the second lens the focus is very much reduced, and the heat, when the sun shines brightly, rendered very intense. The diamond was placed in the focus and anxiously watched. On a sudden Sir H. Davy observed the diamond to burn visibly, and when removed from the focus it was found to be in a state of active and rapid combustion.’
The combustion of the diamond had never been effected by radiant heat from a terrestrial source. I tried to accomplish this before crossing the Atlantic, and succeeded in doing so. The small diamond now in my hand is held by a loop of platinum wire. To protect it as far as possible from air currents, and also to concentrate the heat upon it, it is surrounded by a hood of sheet platinum. Bringing a jar of oxygen underneath, I cause the focus of the electric beam to fall upon the diamond. A small fraction of the time expended in the experiment described by Faraday suffices to raise the diamond to a brilliant red. Plunging it then into the oxygen, it glows like a little white star; and it would continue to burn and glow until wholly consumed. The focus can also be made to fall upon the diamond in oxygen, as in the Florentine experiment: the result is the same. It was simply to secure more complete mastery over the position of the focus, so as to cause it to fall accurately upon the diamond, that the mode of experiment here described was resorted to.