Page:Willich, A. F. M. - The Domestic Encyclopædia (Vol. 2, 1802).djvu/79

Rh decompose them, but at the same time gently contribute to carry off the noxious matter.  COPPERAS, a name given to green, particularly to that of iron. It is purified and prepared in the same manner as alum and saltpetre, being passed through several lixivia, till it is wholly reduced to crystal. It is used in dyeing wool and hats black, in making ink, tanning leather, and in preparing a kind of Spanish brown for painters.

A patent was granted in May 1791 to Mr., of Redruth, Cornwall, for a method of making (from the same materials, and from processes entirely new) copperas, vitriol, and different sorts of dye, or dying stuff, paints, and colours.

The patentee directs any quantity of what remains after the calcination of mundic, or such other as contain sulphur, arsenic, and zinc, to be taken, and washed in water; which is to be placed on the top, or on any other part of the kiln, house, or oven, while the mundic or other ores are burning; the heat of which will cause the water to evaporate; or the water may be evaporated to a crystallizing point, by exposing it to the heat of the sun, after which it should be suffered to stand for 24 hours, or longer, when crystals of copperas, or green vitriol, will be produced. From this process arises a considerable saving; as the ores remaining after fusion, may be applied to various chemical purposes.  CORAL, Corallina, L. a genus of insects, consisting of eight species, which are found in the ocean.

There are, properly, but three kinds of coral, namely, red, white, and black; the last of these is the rarest and most esteemed. When coral is first taken out of the sea, the small protuberances on its surface are soft, and yield on expression a milky juice, which effervesces with acids. The cortical part, or the external coat, is not so compact as the internal, and may easily be separated, while in a fresh state. The greatest traffic in this article is carried on at Genoa and Leghorn.

Coral is not unfrequently imitated, by artificial compositions, so as to resemble the real. But this fraud may be detected, by exposing it to fire; as the counterfeit does not afford the alkaline earth, yielded by the genuine coral. The colouring ingredients employed in preparing the former, are cinnabar and minium, both of which are easily ascertained. The natural coral seems to receive its colour from iron, as spirit of vitriol acquires from it a ferruginous taste; and, on calcination, some particles are discoverable among the ashes, that are attracted by the magnet.

Various unsuccessful attempts have been made to extract a fine colour from red coral, the Isis nobilis, L. by means of spirit of wine. The method of obtaining it is as follows: Dissolve a pound of sugar in a little water, add to it half a pound of wax, then take a pound of coral, and boil them together. Thus, the coral will part with its redness, and remain in other respects unaltered. In order to prepare this tincture, the wax and sugar must be previously dissolved in spirit of wine.  CORALLINE, or Sea-moss, a branched cretaceous substance, of a white colour. It is the habitation and production of polypi, found on rocks, and sometimes on the