of glass.  When, however, the tube containing the boron becomes raised to the temperature, boron sulphide condenses in the portion of the tube adjacent to the heated portion; at first it is deposited in a state of fusion, and the globules on cooling present an opaline aspect.  Further along the tube it is slowly deposited in a porcelain like form, while further still the sublimate of sulphide takes the form of brilliant acicular crystals.  The crystals consist of pure B_{2}S_{3}; the vitreous modification, however, is usually contaminated with a little free sulphur.  Very fine crystals of the trisulphide may be obtained by heating a quantity of the porcelain-like form to 300 deg. at the bottom of a closed tube whose upper portion is cooled by water.  The crystals are violently decomposed by water, yielding a clear solution of boric acid, sulphureted hydrogen being evolved.  On examining the porcelain boat in which the boron had been placed, a non-volatile black substance is found, which appears to consist of a lower sulphide of the composition B_{4}S.  The same substance is obtained when the trisulphide is heated in a current of hydrogen; a portion volatilizes, and is deposited again further along the tube, while the residue fuses, and becomes reduced to the unalterable subsulphide B_{4}S, sulphureted hydrogen passing away in the stream of gas.

Two selenides of boron, B_{2}Se_{3} and B_{4}Se, corresponding to the above described sulphides, have also been prepared by M. Sabatier, by heating amorphous boron in a stream of hydrogen selenide, H_{2}Se.  The triselenide is less volatile than the trisulphide, and is pale green in color.  It is energetically decomposed by water, with formation of boric acid and liberation of hydrogen selenide.  The liquid rapidly deposits free selenium, owing to the oxidation of the hydrogen selenide retained in solution.  Light appears to decompose the triselenide into free selenium and the subselenide B_{4}Se.

Silicon selenide, SiSe_{3}, has likewise been obtained by M. Sabatier by heating crystalline silicon to redness in a current of hydrogen selenide.  It presents the appearance of a fused hard metallic mass incapable of volatilization.  Water reacts most vigorously with it, producing silicic acid, and liberating hydrogen selenide.  Potash decomposes it with formation of a clear solution, the silica being liberated in a form in which it is readily dissolved by alkalies.  Silicon selenide emits a very irritating odor, due to the hydrogen selenide which is formed by its reaction with the moisture of the atmosphere.  When heated to redness in the air it becomes converted into silicon dioxide and free selenium.

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NATURAL SULPHIDE OF GOLD.

By T.W.T.  ATHERTON.

The existence of gold in the form of a natural sulphide in conjunction with pyrites has often been advanced theoretically as a possible occurrence, but up to the present time this occurrence has, I believe, never been established as an actual fact.