pound of starch and water. Starch is not soluble in alkohol.

In the process of converting grain into malt, the starch or fecula is changed into sugar. It may also be converted into sugar by boiling it with diluted sulphuric acid.

Starch consists of carbon, oxygen, and hydrogen. Gluten. This principle is found in various vegetable juices, but most abundantly in wheat flour. It is separated from it by washing, with a stream of water, a paste made of flour and water, at the same time kneading it between the fingers. The water carries off the starch gradually, leaving the gluten behind. Gluten is insoluble in water, and is elastic like elastic gum. It has no taste, and, when dried, becomes hard and brittle. It considerably resembles animal gluten, furnishing ammonia by distillation.

Fixed oil. This is obtained by pressure from certain seeds and fruits, as the olive, linseed, rape seed, almond, &c. The fixed oils differ much; some being nearly solid, are called vegetable butters. When expressed, they are generally mixed with some mucilage, which occasions them to turn rancid. They may be deprived of their colour by charcoal. Fixed oils dissolve sulphur, and then form balsams. They also dissolve phosphorus.

Fixed oils are very combustible, and, when strongly heated, yield olifiant and carburetted hydrogen gases.

They form soaps by being combined with alkali. The best soaps are made of olive oil and soda; but common soaps are made with the animal oils and fat.

in

Transparent soap is made by dissolving soap alkohol, and then concentrating the solution which

is of a gelatinous consistence, by distilling off the alkohol.

Fixed oils are much used for painting, as they are of a drying nature: they are rendered still more drying by boiling them with the oxides of metals, as litharge.

Volatile oil.-This is also called essential oil. Many vegetables afford essential oil by expression, or by distillation. When dissolved in water they constitute perfumed essences and distilled waters. They have much odour and taste. They are inflammable. They are volatilized by a gentle heat, and evaporate entirely when pure so as to leave no trace. The chief essential oils are, the oils of turpentine, spike, cloves, oranges, lemons, lavender, &c. Many of them bear a high price.

Resin.-The resins are an important class of vegetable substances from their application in the arts. They are very numerous, and often exude spontaneously from trees. Common resin is obtained from the fir: a juice exudes from this tree, which is common turpentine: this consists of the oil of turpentine and resin. When the essential oil is separated by distillation, the resin remains. Mastich is a resin obtained from a tree that grows in Turkey. Sandarach is the resin of a tree in Barbary. Copal is a resin from a tree that grows in America, and is a very valuable substance for varnishes. Lac is a resin made by an insect in the East Indies. It is very useful in varnishes, and in sealing-wax. Amber is a substance resembling in its properties the resins, but it is only found in the earth, or washed out and driven on the shores. All the resins are insoluble in water, but soluble in alkohol, especially when assisted by heat. The greater number are soluble in the essential oils, and some are so in the

fixed oils. They are also dissolved by alkaline lys, and by the acids. Resins consist of oxygen, carbon, and hydrogen; and they are supposed to be volatile oils saturated with oxygen.

Bitumen is a substance having some analogy with oils and resins, although differing in its constituents, and being also a mineral body. Pure bitumen is called naphtha, which is transparent, highly inflammable, volatile, of a pungent odour; it is found in certain wells, and there are springs of it in several parts of the world. When naphtha is exposed to the air, it thickens, and becomes dark coloured; it is then called petroleum, which is procured in the same manner, and is used for burning in lamps. Maltha or mineral pitch is a still farther thickened bitumen, and when it has become solid it is called asphaltum. Caoutchouc. This is the substance usually known by the name of Indian rubber, and sometimes elastic gum. It was first brought from South America. It exudes as a milky juice from a tree, which thickens and hardens by exposure to the air. The natives form it into bottles by covering balls of clay with this juice; the clay is afterwards washed out after the caoutchouc is solid. caoutchouc is pure, it is white, the black colour being owing to the smoke used in drying it. This substance is extremely elastic. It is perfectly insoluble in water, but it may be softened by boiling, so that its edges may be united together. It is not soluble in alkohol: but it is soluble in ether; and when the ether is evaporated, the caoutchouc remains unaltered in its properties: by this means tubes and other instruments might be made of it, but the method would be too expensive. It is soluble in some of the fixed and essential oils, as in spermaceti and in oil of cajeput.

When

Woody fibre. When a piece of wood has been boiled in water and in alkohol, until the soluble substances have been extracted from it, what remains insoluble is the woody fibre, or lignin, which is the basis of wood, and consists of long fibres, having a considerable degree of transparency, without taste, and unalterable by the air. It is insoluble in water and alkohol. It is very inflammable; and, when distilled in a close vessel, yields an acid substance formerly thought to be a distinct acid called the pyro-ligneous, but now known to be the acetic acid with an empyreumatic oil. Pure acetic acid or vinegar is now made from wood by distillation. Wood consists of oxygen, carbon, and hydrogen; when burned, the carbon remains, constituting charcoal.

Colouring matter. - The colours of vegetables are owing to peculiar matters, which are extremely numerous, and but little known. Many of them are used as dyes and pigments. The extraction of colouring matters from vegetables, and fixing them on cloths, constitute the arts of dyeing and calicoprinting (which see). The colouring matters sometimes are inherent in gums, sometimes in resins, sometimes in fecula; consequently they require different chemical agents for their solution. Tannin. This principle is so called because it is employed in the art of tanning leather. It is also called the astringent principle. It is found abundantly in the barks of several trees, particularly the oak, and also in certain seeds. The gallnut and grape-seeds afford very pure tannin; and a substance called catechu, from India, consists chiefly of it. Tannin is distinguished by its forming a precipitate with glue, or isinglass. This precipitate is insoluble in water, and is that which

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is formed when skins are tanned and made into leather.

Wax. This substance appears to be formed by bees, by some animal process. It is also a vegetable substance, for the polish or varnish of leaves is owing to a coating of wax; and in some vegetables in Brazil wax exists in considerable quantity. Wax is insoluble in water, but sparingly dissolved by boiling alkohol. It is dissolved readily by the fixed oils, and then forms cerates and ointments. Wax contains a large proportion of carbon, with hydrogen and oxygen.

Camphor. This substance is brought chiefly from Japan, and is distilled from a species of laurel. It is white and semitransparent; it is very inflammable, soluble in alkohol, and sparingly so in water. It is very volatile, and capable of converting into an acid, called the camphoric acid, which form neutral salts called camphorates. Camphor resembles essential oil in many of its properties.

Bitter principle. It is supposed that this is a peculiar principle. It exists in many vegetables, particularly in quassia, gentian, hop, &c. When extracted, it is of a brownish yellow colour, and brittle when dry. Its taste is very bitter. It is soluble in water and alkohol. A variety of it is supposed to exist in unroasted coffee.

Narcotic principle. -This has lately been called morphine, and is found most abundantly in opium, which consists of this together with several of the principles which have been just described. It is a violent poison when taken internally. When pure

it is white, without taste or smell. It is soluble in boiling alkahol, but is scarcely acted upon by water. From the rapid progress of chemistry, many other vegetable substances are considered as pe