That imported from China is purer than that from Thibet, and is found in a natural state, in small masses of irregular crystals, of a faint white colour. Borax is useful in metallurgy, for soldering, in the fusion of vitrifiable earths, with which it forms glass; as also in several other chemical processes; and dyers frequently employ it for giving a gloss to silks.

(24) The veins which afford metallic substances are fissures more or less vertical, filled with a material different from the rock in which they exist, and generally extending from east to west. A brown powder at the surface of a vein always indicates iron or tin; a pale yellow powder, lead; and a green colour in a vein, or in water, denotes the presence of copper.

(25) Precipitation or coagulation is an operation the very reverse of solution, and is the bringing a body suddenly from a fluid to a solid state.

(26) The blue opaque substance called Turquoise, worn for ornament, and generally considered a stone, is the tooth of an animal penetrated by the blue calx of copper, which may be extracted from it by distilled vinegar. It is principally found in Persia and France.

(27) The Alluvial formation consists of the loose earthy soil which covers the solid rocks, or which, by

being separated by water, air, &c. is deposited in beds.

(28) Silicious earth, or silex, or quartz, is hard, and resembles glass; when pure it does not melt by itself in heat, and after burning does not fall into a powder like calcareous earth. It excites no effervescence with acids, and in the fire it melts very easily to glass, with a fixed alkaline salt.

(29) Smalt is a species of glass of a dark blue colour, a preparation of calcined cobalt, with pulverized flint and potash. It is used in many arts and manufactures, and by clear starchers, under the name of powder blue.

(30) The cobalt is first to be mixed with a solution of

nitro-muriatic acid, and this fluid is then to be so diluted with rain water as to prevent its staining paper when applied upon it. The paper ought to appear white when cold, and become green on being heated. Landscapes may easily be formed to represent the dreary season of winter, by only shading with Indian ink, and the scene be soon changed into the rich verdure of spring by application of a slight degree of heat, where the sympathetic ink has previously been brushed over the parts thus traced. If it remain heated too long the green will become fixed.

(31) Oxyde is a term used to express a numerous class of

bodies, formed by the union of certain bases with a smaller proportion of oxygen than is required to convert them to acids; the principal of which were formerly called metallic calces, and have for their base some metallic substance. Metals are converted into oxydes by combustion, or by solution in acids; and many of them assume this form from the action of the atmosphere alone, but more easily when this is assisted by moisture.

(32) Oils by expression are obtained from the seeds, leaves, fruits, and barks of plants, which, being pounded in a mortar, the oil is forced out by means of a press, without the aid of heat. Such are the oils of olives, almonds, linseeds, &c. As a proof of the time these oils may be preserved, two glass jars of olives and olive oil have been dug up at Pompeii quite fresh and fit for use. It has been asserted that the plague may be checked by anointing the body with olive oil, and that it is a cure for the bite of a viper, and a powerful antidote to various poisons.

(33) There is a range of chalk hills in Berkshire, part of them called the Vale of White Horse, from the figure of a gigantic horse being rudely sketched on the side of one.

(34) Whiting is chalk powdered and well washed; this mixed into a thick paste with Linseed oil is called

putty, and is used by glaziers and painters. The powder of calcined tin, used for polishing iron and steel, is frequently called putty.

(35) Ochre is a genus of earths of various colours; a combination of alumina and red oxyde of iron. These colours are of great use in oil and water painting, and the hues may be varied by means of fire. Ochres are found more abundantly in England and Italy than in any other part of the world.

(36) The wood called Citron wood, and used by turners in France and Germany, is not from the Citrus, but the wood of an American tree called by the natives Candle wood, as it will burn when cut into splinters in a similar manner to a candle.

(37) Argentiere or Cimolus is one of the Cyclades, a cluster of islands near Delos, in the Archipelago.

(38) The terms applied to diamonds, are first, second, or third water, according to their value; and the name of Oriental and Occidental is given to this and other precious stones, not in reference to their being the production of the east or west, but only to denote their value; the latter term being applied to inferior stones.

(39) Pyrites is a genus of inflammable substances, composed of sulphur which has dissolved itself with

metals. There are many kinds, as of iron, copper, gold, &c.

(40) Aqua is a name frequently applied to particular medicines or menstruums, in a liquid form; among the numerous varieties distinguished from each other by an additional term, is aqua fortis, which is a mixture of nitrous and vitriolic acid, and is of great use to dyers and artificers, from its dissolving powers. Aqua regia is a combination of nitrous and marine acid, and is particularly useful in dissolving all metals except silver.

(41) Beta, or Beet, a plant of which there are several species very common in England, and principally cultivated as food for cattle.

(42) Mandragora is a species of Atropa, or Deadly Nightshade.

(43) Galls are protuberances formed upon different trees by insects of the fly kind, which by degrees become hardened by the air. The oak galls are most esteemed for ink, as they impart a dark purple or black colour to vitriol and water. The most superior galls are brought from Aleppo.

(44) There are two kinds of lamp black; the best is obtained from resinous matters, from the soot which arises in the burning the dregs and pieces of bark