CRYOLITE

CRYOLITE, alumine fluate alkaline, Haily; cryone, halloide, Haidinger.

This rare mineral is of a snow-white colour. It was originally brought by a missionary from Greenland to Copenhagen, where, from its resemblance to the common varieties of the sulphate of barytes, it lay neglected for many years.

At length Abildgard, attracted by its peculiar ponderosity, was induced to undertake its examination, in the course of which floric acid, hitherto known only as a component of fluor spar, presented itself along with alumine; but as a considerable residue remained unaccounted for, Klaproth repeated the investigation, and discovered the presence of thirty-six per cent. of soda.

Of the geognostic relations of this interesting mineral nothing was known till the late Sir Charles Giesecke visited the locality, which he found situated on the west coast of the peninsula, in a fiord or arm of the sea, denominated Arksut, near a place called Ivikaet, where it occurs in two contemporaneous beds disposed in gneiss, nearly parallel to each other, and at no great distance.

Fragments of cryolite obtained by cleavage are too often called crystals; but nothing of the kind has hitherto been observed. Its cleavage, however, is very distinct after being well soaked in water: it is threefold, two of these forming rectangular prisms with very smooth surfaces, while the third is at right angles to these, and rougher. Its great fusibility, for it yields even to the flame of a candle, suggested to Abildgard the name of cryolite, taken from κρύος, ice, and λίθος, a stone, which it has always retained. It contains, according to—

and possesses a specific gravity of 2.949.

CRYOPHORUS (κρύος, frost, φῶς, to bear), a name given by Dr Wollaston to an instrument of his invention, which serves to illustrate the theory of heat. The form of this instrument may be readily conceived without a figure. It is a glass tube, bent at each end, the bent parts terminating in hollow glass balls, D and E. The ball D is half filled with water. A vacuum is produced in the tube and ball E, by boiling the water in the ball D, whilst the capillary aperture in the ball E, through which the steam is issuing, is held in the flame of a lamp till the steam becomes

Crypt weak enough to allow the melted glass to collapse and seal up the capillary aperture. The apparatus is now allowed to cool, when the ball D will be half full of water, and the ball E, and the rest of the apparatus, will contain transparent watery vapour. If now the ball E be placed in a freezing mixture of salt and snow, the water in the ball D will be speedily frozen. The cold of the freezing mixture produces this effect by condensing the aqueous vapour in the ball E, and thereby producing a vacuum in the part not occupied by the water; thus taking off the pressure from the water in D, so as to allow another portion of that water to assume the state of vapour, a change of form attended with a reduction of heat, or a production of cold. That sensible cold accompanies the passage of a liquid to the state of vapour, may be seen by swinging a thermometer at the end of a string, the bulb having been previously wetted with sulphuric ether: the rapid evaporation of the ether causes the mercury to contract to the volume which it has at the freezing of water, or even lower.

The phenomenon exhibited by the cryophorus is of the same nature as that produced on a great scale by means of the air-pump in Professor Leslie's experiment, as described under HEAT.