[Continued page from 158]CRYSTAL OF COPPERAS, OR SULPHATE OF IKON.—This substance, so largely used in the arts for dyeing, &c, and also in chemistry and pharmacy, is obtained, as a natural product, from aluminous chalybeate springs, as well as by the spontaneous decompositon of certain native sulphurets of iron, or iron pyrites; and is prepared in large quantity by the action of air and water. The sulphur and iron are thus both oxidated ; and sulphate ot iron; or copperas, is obtained by crystallizing the lixiviated masses. Crystallization, and the circumstances under which it takes place, form an interesting subject of inquiry. Not having the operations of nature open to our inspection, our only sources of information relative to the formation of crystals are those afforded by the process of crystallization; and here, until very re-cently, our experiments were circumscribed by a very few modes of operation; that of the deposit of crystals from solution in some fluid,; their production while gradually cooling from a state of fusion; and their volatilization by heat, or otherwise. Latterly, however, by the aid of that universal agent— electricity—new methods ot producing crystals have been pursued; and there can now be little doubt that all ii# phenomena of crystallization are governed, in a greater or lesser degree, by electric influence. SPECIMENS OF CRYSTALLIZED ALUM AND BICARBONATE OF SODA.—The first of these products is also extensively used in the arts, as well as in chemistry and medicine. It is an earthy salt, and occurs in a native state only in small quantities. In a great measure, however, it is prepared artificially from alum slate—a. rock belonging to the coal formation and containing a considerable proportion of sulphur, iron, and alumina. The slate is broken in pieces, roasted, exposed to air and moisture; and, the soluble parts being dissolved in water, crystals of alum are obtained as the solution cools. Bicarbonate of soda is chiefly used io medicine, and may be obtained by passing carbonic acid through a concentrated solution of the carbonate. CAMPHOR AMD BORAX.—Camphor is one of the principles arising from the separation of the volatile oil of two trees; the one, a native of Japan and China; the other, a native of Borneo and Sumatra. From these it is procured by different processes. It exists in every part, root, stem, branches, and leaves of the first-mentioned tree, which is chopped into pieces sufficiently small to be thrown into iron vessels. These vessels are afterwards covered with earthen hoods, in which are placed rice, straw, and rushes ; heat being subsequently gradually applied. The camphor is volatilized, and afterwards condenses on the straws, rushes, &c. This, alter being purified from the intermixture of straw, is found in commerce under the name of crude camphor; but it still retains many impurities, and on arrival in Europe is refined. The tree is familiarly known in this and other temperate countries as an ornament of conservatories. It is a graceful evergreen tree, whose wood and leaves emit, when bruised, an agreeable camphorous odor. In the camphor tree of Borneo, on the contrary, the volatile oil is not procured by distillation. The camphor here occupies the pith of the tree, existing in its stem, in a crude solid form, along with camphor oil, Camphor has been long and extensively used in medicine; but even yet its physiological and therapeutic actions have not been fully discovered, from the fact that more systematic inquiries have not been made as to its medicinal results. Borax is, in reality, a compound of boracic aciJ and soda, correctly termed biborate of soda. It is chiefly brought from the East Indies, Persia, and Ceylon, and also from a lake in Thibet entirely supplied by springs, where it is collected by the natives from the edges in a state of crystalKfclion. It is imported under the name of tineal. The crystals are bluish, or greenish-white, and sometimes nearly transparent, as well as soft and brittle. It is purified by solution in water and crystallization, and is then sold as borax. On the continent, borax is prepared by decomposing carbonate of soda with the boracic acid of Tuscany, and purifying the biborate by various processes. Little is yet known of the medicinal actions ol borax. Its chief use in the arts is for glazing porcelain and making green fire. FERROCYANIDE OF POTASSIUM, USED FOE. DYEING BLUE, IN PLACE OF INDIGO.—This is perhaps one of the most important chemicals used in the art of dyeing, and calico printing. Its preparation consists in projecting a mixture of pearl ashes with hoofs, horns, and other animal matters, in the proportion of two to five, into a red-hot iron crucible, and stirring diligently the pasty mass thus formed until fetid vapors cease to arise from it.— When the product has cooled, it is lixiviated with cold water, filtered and concentrated, upon which yellow crystals of ferrocyadine of potassium are tormed. By the addition of a salt of iron to ferrocyadine of potassium, that most beautifnl blue, called Prussian blue, is produced. PYRAMID OF BEST TABLE SALT, WITH SEVERAL OTHER SPECIMENS OF SALT.---These specimens of salt were from the extensive mines of Northwitch, in Cheshire, where there are also brine springs. They are of two binds—the one white and transparent, tne other ot a reddish-brown. The rock salt is found from 28 to 48 yards beneath the surface of the earth. The first stratum is from 15 to 20 yards in thickness, extremely solid nd hard, resembling sugar candy. Many tons at a time are loosened by blasting with gunpowder. The second stratum is ot hard stone, from 25 to 35 yards in thickness. The salt lies beneath this stratum in a bed above 40 yards thick, generally perfectly white, and clear as crystal. It is stated that the annual production of salt in England is upwards of 800.000 tons, and the population engaged in its manufacture 11,000 to 12;000. The sources of supply are said to be inexhaustible; and latterly the salt manufacturers have so lar extended their works that the opening ofa new market would be of the greatest advantage.— Common salt, for ordinary purposes, can now be obtained at about 20 shillings sterling per ton. In India, the British government monopolizes both the manufacture and sale of salt, and the exportation of British salt to India is prohibited. Attempts have been made by the salt manufacturers and ship owners to obtain admission for British salt into the ports of India at a moderate duty; and the latter, especially, complain of the disadvantage of not being allowed to take so convenient an article of merchandise to that part of the British empire. The salt monopoly had existed in India long before the sway ot the East India Company commenced ; aad its modification, and total abolition, is considered only as a question of time. It is believed that a moderate duty on salt would soon yield quite as large a revenue if the monopoly were abolished, while commerce would be benefitted by the exchange of sugar and other commodities for salt; smuggling in salt, which is extensixely carried on, would cease; and, in place of arbitrary and harsh restrictions, the consumer would obtain a better article at a much cheaper rate. REFINED INDIGO.—This substance is the innoxious and beautiful product of an interesting tribe oi tropical plants, and is very extensively employed in dyeing and calico printing; being, esteemed the most useful and substantial ot all dyes. When the plant is in full flower it contains most coloring matter. It is then cut, dried, and put into vats, and covered with water ; fermentation takes place, accompanied with the evolution of carbonic acid, and other gaseous products, and the yellow liquor is covered with a froth.' This froth, in a little time, becomes of a violet color, and a substance is evolved which is rendered blue by absorbing oxygen of the air, and, being thus rendered insoluble, is precipitated. This, when, collected and dried, is indigo. SPECIMEN OF ULTRAMARINE.—This is a well known blue pigment of extraordinary beauty. Until within the last few years it was entirely prepared from the lapis lazuli, or lazulite, and from the great costliness attending its preparation, its use was confined to the artist. It is now prepared, artificially, at a very moderate rate, and equal in beauty to that obtained from the lazulite. It is stated that by adding freshly precipitated silica and alumina, mixed with sulphur to a solution of caustic soda, evaporating the mixture to dryness, and placing the residue in a covered crucible, and exposed to a white heat, where the air has a partial access to it, a pure ultramarine is obtained. The product is then reduced to impalpable powder. The proportions of materials to be used are about 36 silica, 36 alumina, 24 soda, and 3 sulphur. Since this discovery, its value has become very much reduced, and it is now used extensively in the arts.