Tavernier observed that the color of the diamonds in India often partook of the color of the gravel in which they were deposited,--white, reddish, blackish, or greenish, according to the color and purity of the matrix. This fact has also been noticed in Brazil; and it lends support to the view that the gems have been deposited under stagnant water, and have received some tinge from its color. The diamond is admitted by microscopists to be one of the foulest gems known to them; and specimens are rare that do not exhibit cavities, imperfections, or foreign matter in their interior. A painstaking microscopist, after examining the large collection of rough crystals of the East India Company in London, which numbered several hundred specimens, came to the following conclusion: “It seems to be a general truth that there are comparatively few diamonds without cavities and flaws, and that the diamond is a fouler stone than any other used in jewelry.” Berzelius first called attention to a black substance which he found in a diamond belonging to the collection of Countess Porlier; and since then many other examples have been observed. Frequently black specks resembling anthracite have been noticed in the Brazilian diamonds. Tavernier saw in India a large diamond of one hundred and four karats, whose central portion was so foul as to render the stone worthless. When it was cut open the cavity yielded about eight karats of filth, resembling that of a rotten weed. The diamond is now recognized by the chemist as a crystalline form of pure carbon. Newton, in 1675, with the wonderful penetration of his genius, and reasoning from the high refractive power of the gem, which so far exceeded the degree due its density, believed it to be combustible. More than a century later the experimentalists of the Academy of Florence strengthened this view by destroying it in the focus of powerful burning mirrors. Lavoisier, however, dispelled all doubts concerning its combustibility by burning it under a receiver filled with oxygen gas. It has since been ascertained that a temperature of 14° Wedgewood completely volatilizes the diamond, producing carbonic acid gas. An English experimentalist, however, has recently declared that the gem may be consumed at a red heat, and maintains that he has accomplished this result by enveloping the stone in certain alkalies.