“Brown diamonds lose most of their color when heated to whiteness in hydrogen; they generally assume a grayish tint, and in all cases the shade is much lighter, and on examination with a lens they appear limpid, with black spots. Diamonds with a yellow tint, such as Cape diamonds almost invariably are, scarcely lose any portion of their natural color.... Several experiments were made by von Baumhauer, in concert with M. Daniels, upon gray diamonds, in the hope that the effect of heat would, by removing their color, add to their value; but, unfortunately, the desired result was not achieved, as the diamonds presented after treatment the same grayish appearance as before. Very different results are obtained when, instead of heating the diamond in an atmosphere of hydrogen, it is heated in contact with the air. It is unnecessary to employ a white heat, or to subject the diamond to it for so long a time, in order to render it dull, and consequently opaque; this being the result of positive combustion, which is proved by its loss of weight after the operation. “This combustion is, however, quite superficial, as shown by M. Daniels, who found that when repolished the diamond recovered completely its transparency and its water; it was, moreover, remarked by Mr. G. Rose that if the diamond which had become dull was moistened with essence of turpentine, it reassumed its transparency and retained it so long as its surface continued moist. The diamond may also be heated in an atmosphere of oxygen.... In this case the stone obtains a vivid state of incandescence, and burns with a dazzling flame long before the platinum crucible has attained a reddish white heat. In most cases after the lamp has been withdrawn and the crucible is no longer red hot, the diamond continues to burn for some time, and presents the appearance of vivid light upon a dark ground. When the diamond is very small combustion may even continue until it is entirely consumed, and it is then seen to dart a more vivid flame at the last moment, like a burning match, the instant previous to extinction. When the stone is of considerable size the heat produced by combustion is insufficient to maintain it after the removal of the lamp, and it ceases in a few moments, notwithstanding the oxygen which continues to flow into the crucible. Although this last experiment has been repeated several times by these experimentalists, no other result has been observed than tranquil combustion of the diamond; such phenomena as turning black, transformation into coke, change of the state of aggregation, bubbling up, melting or softening, rounding of corners and angles, were in no case presented to our notice. Once only in experimenting upon an opaque grayish diamond, a few sparks were emitted, but these were evidently due to the presence of some foreign elements incorporated with the whole. Neither did the diamonds burst