SPINELLANE. SPINTHERE. HIDROGEN GAS.

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Species 98. Spinellane. Havt.

It occurs in hexaedral prisms, terminated by three-sided summits,whose faces stand on alternate, but different, lateral edges at each ex-tremity ; the edges of the summits are sometimes truncated. ItScratches glass, and has a blackish brown color. /

Before the blowpipe it becomes white, and easily melts into a veryporous enamel.

It is found on the banks of the lake Laach, department of theRhine and Moselle, in a rock, composed chiefly of feldspar with quartz,hornblende, mica, and magnetic iron.

Species 99. Spinthere. Havt. Jameson.

Its color is greenish gray ; and its crystals at first view somewhatresemble green axinite. They are small and have a strong lustre ;their form is an irregular, double four-sided pyramid, whose summitsare obliquely truncated. It has a foliated structure, is translucent atthe edges, and too soft to scratch glass.—It is easily melted by theblowpipe.

It has been found in Dauphiny, its crystals being attached to cal-careous spar.

CLASS III.

Combustibles.

All the minerals, which belong to this class, combine with oxigen,and undergo combustion. Their physical properties sufficiently dis-tinguish them from metals, which, strictly speaking, are also com-bustibles.—They are sometimes gaseous, sometimes liquid, and some-times solid. In general, they have a low specific gravity, and areeasily broken. They are seldom crystallized. Their colors, in mostcases, depend on the nature of the mineral, are hence few in num-ber, and form important characters; they are usually some shadeof black, brown, or yellow.

Carbon, hidrogen, and sulphur, either singly, or in combinationwith each other, constitute the principal ingredients of these com-bustibles ; a little oxigen, or iron, or some earth is often present.

Species 1. Hidrogen Gas.

This gas is twelve or thirteen times lighter, than atmospheric air.It takes fire on the approach of flame, and burns silently, unlessmingled in certain proportions with air or oxigen, in which cases itburns with an explosion. This gas, seldom or never found pure, usu-ally holds carbon or sulphur in solution, thus forming the two follow-ing subspecies.

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