Experimental Researches in Chemistry and Physics/Apparatus for the combustion of the diamond
Description of a New Apparatus for the Combustion of the Diamond[1].
In the course of the experiments which Sir Humphry Davy made at Florence on the combustion of the diamond, he discovered that when the gem began to burn in an atmosphere of pure oxygen, having free access to it on all sides, it would continue burning, though the original source of heat were removed, until the particles were rendered so small as to be too readily cooled by the little platinum tray which supported them. (Philosophical Transactions, 1814, p. 557.) In consequence of this observation, an idea arose, that if the diamond were well heated, and then introduced into oxygen, it would go on burning, and afford an easy method of exhibiting its combustibility. Upon trial this was found to be the case, and a notice to that effect put in this Journal (see shove). Since then, an apparatus of this kind has been perfected, and is now represented in Plate I. fig. 1.
It consists of a glass globe, of the capacity of about 140 cubic inches, furnished with a cap, having a large aperture; the stopcock, which screws into this cap, has a jet A rising from it, nearly into the centre of the globe; this is destined to convey a small stream of hydrogen or other inflammable gas. Two wires, c c, terminate at a very little distance from each other, just above this jet, and are intended to light the stream of hydrogen by electrical sparks; one of them commences from the side of the jet, the other is enclosed and insulated nearly in its whole length in a glass tube: the tube and wire pass through the upper part of the stopcock, and the wire terminates on the outside in a ball or ring, D, at which sparks are to be taken from the machine, either directly or by a chain. On the end of the jet is fixed, by a little socket, a small capsule, B, made of platinum foil. This capsule is pierced full of small holes, and serves as a grate to hold the diamonds. Its distance is about three-quarters of an inch from the end of the jet; and the arm, by which it is supported, is bent round, so that the stream of hydrogen shall not play against it. The stopcock screws, by its lower termination, on to a small pillar fixed on a stand, and at the side of this pillar is an aperture by which a bladder filled with gas may be connected with the apparatus.
On using the apparatus, the diamond is to be placed in the capsule, and then the globe being screwed on to the stopcock, the latter is to be removed from the pillar and placed on the air-pump; the globe is then to be exhausted and afterwards filled with pure oxygen: or, lest the stream of oxygen in entering should blow away the diamond, the globe may be filled with the gas first, and then, dexterously taking out the stopcock for a short time, the diamonds may be introduced and the stopcock replaced. The apparatus is then to be fixed on the pillar, and a bladder of hydrogen gas attached to the aperture. Now, passing a current of sparks between the wires, a small stream of hydrogen is to be thrown in, which inflaming, immediately heats the capsule and diamonds white-hot; the diamonds will then enter into combustion, and the hydrogen may be immediately turned off and the bladder detached. The diamonds will continue to burn, producing a strong white heat, until so far reduced in size as to be cooled too low by the platinum with which they lie in contact.
When the flame of hydrogen is used to heat the diamonds, it is evident a little water will be found in the globe; but this is of no consequence, except in attempts to detect hydrogen in the diamond; the inconvenience may be obviated, if required, by using the flame of carbonic oxide. As, however, no hydrogen has at any time been detected in the diamond, it is better to use that gas as the heating agent; for then the carbonic acid, produced by the combustion, is unmixed with that from any other source, and may be collected, and its quantity ascertained.