This stone, when burned, forms a cement which has the property of setting very strongly under water. It has also, of late years, been employed in a manner which merits particular notice, for the multiplying of copies of drawings and penmanship. A drawing is made on prepared paper with a peculiar kind of ink. A slab of lias, about an inch thick, is then heated; the drawing is placed upon it, and both are passed through a rolling press. The paper is afterwards wetted, and washed from the stone; but the ink, being of a gummy or glutinous quality, becomes in part absorbed by the stone, and remains. The stone is then ready for the printer. Previously to taking off each impression, the stone is wetted with a sponge; fresh ink (which is said somewhat to resemble printers’ ink, and is put on with a ball similar to that used by letter─press printers) is then applied. This is prevented, by the water, from adhering to any part except to the ink that had been absorbed, by the stone, from the paper on which the drawing was originally made. Paper is then placed on the stone, both are passed through a rolling press as before, and a perfect impression of the drawing is made upon the paper. This art has been practised in Germany with great success; and with the difference only of the original drawing being made upon the stone instead of paper. Many beautiful specimens of drawings, taken from slabs of lias, may be seen in this country. It is said that copies of military drawings and orders were, to a very large amount, multiplied by this means at the headquarters of the armies lately employed on the Continent. An artificial composition is sometimes used instead of lias. Considerable quarries of this stone are wrought in Germany. It is also found at Leixlip, near Dublin; in beds at Aberthaw, in Glamorganshire; in Dorsetshire, and near Bath. SULPHAT OF LIME. 192. _ALABASTER, or GYPSUM, is a kind of sulphat of lime, or of lime in combination with sulphuric acid (24), which has a shivery and glittering texture; and is of white colour tinged with grey or red, and sometimes striped, veined, or spotted. When crystallized, the primitive form of its crystals is a regular four─sided prism_ (Pl. II, Fig. 14.) Being considerably softer than marble, this mineral is not capable of receiving a good polish. From this circumstance it is, however, the more easily worked. It is manufactured into chimney─pieces, columns, busts, ornamental vases, and lamps; the latter of which transmit a soft and pleasing light. Such is sometimes the transparency of alabaster, that it has been employed for windows; and, at Florence, there is now a church which receives its light through the medium of this substance.