PROOFS OF THE COMBUSTIBILITY OF DIAMOND.

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became completely black and of a coally appearance ; the instantafterwards, brilliant and as it were boiling points were distinctlyperceived on the black ground. It now began to diminish insize and in a short time no more than one-fourth was remain-ing. It was then withdrawn. It was without any marked sharpangles or edges, but still very white, and of a beautiful transpa-rency. The diamond was a second time heated with the solarrays, and in twenty minutes entirely consumed without any re-sidue. During this operation the same phenomena were ob-served.

A solution of barytes was then introduced over the mercuryconfining the air in which the diamond had been consumed. Itbecame immediately milky, the volume of the gas diminished,and carbonate of barytes was formed.

In this process a greater quantity of carbonic acid was ob-tained, than would have been produced, had the diamond beenin the same state as common charcoal. For one part of char-coal absorbs during combustion 2.527 of oxigen, and produces3.5/5 of carbonic acid; but one part of diamond absorbs some-what more than four parts of oxigen, and produces five of car-bonic acid.

The diamond of which Guyton effected the complete combus-tion was a native octohedral crystal. It burned in a tempera-ture of about 90 pyrometrical degrees, which in the scale ofWedgwood constitutes a difference of from 183° to 1765 0 .

We are likewise indebted to Dr. Smithson Tennant for someexcellent experiments on the nature of the diamond. His paperof which we shall give an abstract is in the Philosophical Trans-actions for 1797- Dr. Tennant has taught us a method of effect-ing the combustion of the diamond in a much easier manner thanthat stated above. He has proved that by means of nitrate ofpotash, the combustion may be accomplished in a moderate heat.

The Doctor procured a tube of gold, which having one endclosed, served as a retort, to which a glass tube was adapted inorder to collect the air produced. To be certain that the gold