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An adhesive, gummy, resinous substance, prepared by inspissating tar, of wbich large quantities are prepared in Great Britain. The best Pitch is imported from Norway and Sweden ; it is of a shining black colour, dry, and brittle, and is principally employed by ship-builders, as a cement or defence for wood and other substances. On account of its stimulating properties, plasters are frequently made of it for colds and coughs. In boiling the tar to Pitch an esseutial oil is obtained, which is used by painters and varnishers, as it possesses drying properties. There are various kinds of Pitchamong them the Mineral Pitch or Barbadoes Tar, also called Rock Oil; this is a thick mineral fluid, found trickling down the sides of mountains, and floating on the sea in America, India, &c.Pitch-Stone or Asphaltum, a bituminous stone, found near Babylon, and used in the composition of cement, which water cannot penetrate. An oil is extracted from this substance, used as Pitch, and also medicinally.-Jew's Piteb or Asphaltos, found about Judea and the Dead Sea, employed by the Egyptians for embalming dead bodies, &c.Pitch Blende, &c.
A name generally given to bodies luminous in the dark, without emitting heat or flame. It constitutes a part of all organized bodies, whether of the animal, vegetable, or mineral kingdoms. Solar phosphori become luminous when removed from sunshine into a dark room. The flesh of salt water fish before it putrifies, and decayed wood, are spontaneously phosphorescent. The luminous appearance upon putrified fish arises from the numerous animalcula which the putrefaction has promoted, and not from the flesh of the fish. Its combination with earths and metals are called phosphurets. Many amusing experiments are performed with this luminous body, but as it will kindle into a flame by slight friction, great care is required in using it. Phosphoric Acid is composed of Phosphorus united with oxygen, and is easily extracted by calcination from bone ashes.
The skins of sheep or goats, rendered subservient by proper preparation to the purposes of binding
books, writing upon, &c. When the wool is stripped off, the skin is steeped for some hours in a lime pit; it is then drained, stretched upon a frame, and the flesh is scraped off with an iron instrument. It is again moistened, sprinkled with powdered chalk, rubbed with pumice stone, drained, and scraped. This process is repeated a third time. The side from which the wool is taken undergoes similar operations, and when the skins are reduced to one half of their original thickness, they are rendered smooth by pumice stone. The parings are used for making glue, size, &c. The manufacture of this article is very ancient, and its invention is generally ascribed to a King of Pergamos; but it appears that prior to his reign, the Persian records were written upon skins prepared similarly to those of the present day. Before the introduction of printing (52) all the manuscripts which handed down to us, are either upon Parchment or Vellum. Vellum is a superior kind of Parchment, prepared from young calf skins, in a similar way to Parchment, except that they are not immersed in a lime pit. A superior glue is obtained from the shreds of Vellum. On account of their durability, both are used for deeds, writs, &c. and a method has been discovered of rendering writing legible upon them when damaged.
A metallic substance discovered in South America about the middle of the 18th century, and found particularly about Choco. It is of a white colour resembling silver, from wbich it derives its name: the diminutive of Plata meaning silver in the Spanish language. Itis heavier than gold, and harder than iron, but extremely ductile, which enables it to be rolled into leaves like gold. It possesses the property of soldering without mixture-it resists the action of acids, alkalies, and sulphur-and it retains its metallic lustre without tarnishing by exposure to the air. It is very difficult of fusion, and when properly refined, its colour is between iron and silver, and without smell. As it resists the force of fire the best crucibles are formed of it, and as a mirror it reflects but one image, and is as unchangeable as glass. Copper is improved by alloying it with Platina, and brass with Platina forms a compound not liable to tarnish. Platina is generally found united with gold, quartz, sand, &c.
The fruit of the Pumica or Pomegranate Tree, about the size of an orange, with a bard rind, filled with soft pulp, and numerous seeds. It grows upon a tree, the stem of which rises to 18 or 20 feet; and the branches are terminated by most beautiful large red flowers, wbich are succeeded by the fruit. There is another species, with double flowers, the fruit of which, as also the flowers, are used medicinally,
QUICKSILVER, OR MERCURY.
One of the perfect metals, and the only one naturally found in a fluid state. The most intense degree of cold will alone reduce it to solidity. There are two properties found in Quicksilver equally wonderful. It takes every form one wishes to give it; but it always ends by reassuming its own natural form. In the fire it rises into vapour. When it is shaken for a considerable time, it changes into dust. By being dissolved, it becomes a hard and transparent crystal; but it can always be restored to its former fluid state. It is discovered in semi-indurated elay, in sandstone, and in other earthy productions ; sometimes in globules, but generally attended with a red substance. The ores from which the greatest quantity is obtained are called Cinnabar. They are of a light or brown red colour, some are dull, and others bright and shining. They are not generally distributed, but when found are in considerable quantities, as at Idria, Almaden, and Deux Ponts. Quicksilver is fourteen or fifteen times heavier than