too, the rosin is freed from any water it may contain. The quantity of rosin obtained is rather less than four-fifths of the resin used.

French turpentine is almost entirely consumed in France; very little is now exported into England. Its properties will be discussed later on.

Russian turpentine is obtained chiefly from the Scotch pine, Pinus sylvestris. The method of obtaining it does not differ essentially from that adopted in extracting American or French turpentine, although there are some minor differences in the method of tapping the trees and collecting the crude resin, and in the manner of distilling the turpentine, which is usually done in a rather crude manner.

Russian turpentine differs slightly in properties from American and French turpentines.

Turpentine is a hydrocarbon having the formula C10 H16 there are, however, a number of isomeric compounds known which have the composition represented by the above formula. These bodies have been named the terpenes; they are derived, as well as the three varieties of turpentine already described, from natural resins or from various natural oils.

They closely resemble one another in their chemical as well as in many of their physical properties. The terpenes have been investigated by Berthelot, Tilden, Wallach and other chemists, and a number of them are known. Berthelot pointed out that French turpentine had some different properties from American turpentine, although their chemical composition was the same. He named the terpene of American turpentine, australene, and that from French turpentine, terebenthene; while he gave to the characteristic hydrocarbon of Russian turpentine the name of sylvestrene. Armstrong considers that American turpentine is a compound of two terpenes, one of which is the same as found in the French turpentine and which rotates a ray of polarised light to the left; this he names lævoterebenthene. The other terpene has similar properties, only it rotates the ray of polarised light to the right; this he names dextroterebenthene; it is found in a very pure condition in the turpentine from Pinus Khasyana, a Burmese tree. Wallach describes nine terpenes which he names-1. Pinene, the main constituent of French and American turpentine. 2. Camphene, which differs from all other terpenes in being solid; it is not found naturally, but can be prepared by artificial means from pinene. 3. Fenchene, which is also obtained artificially. 4. Cimonene, found in the essential oils of various species of

aurantiaceæ, oils of lemon, orange, bergamot, &c. 5. Dipentene, found in oil of camphor, Russian and Swedish turpentine, &c. 6. Sylvestrene, the characteristic terpene of Russian and Swedish turpentine. 7. Phellandrene, found in various essential oils. 8. Terpinene, found in several oils. 9. Terpinonlene, a rare terpene. The two most important of these are Pinene and Sylvestrene, which are found in the chief commercial turpentines.

Pinene is a colourless or water-white mobile liquid of a peculiar and characteristic odour, having a specific gravity of 0.8749 according to Tilden; Wallach gives it as 0.860. It boils at from 155° to 156° C. When dry hydrochloric acid gas is passed into it, combination ensues, and a crystalline body having the formula C10H16 HCl is formed; this closely resembles camphor in appearance and is known as artificial camphor; by heating, under pressure, with caustic potash this body is decomposed and the solid terpene, camphene, is formed. When pinene is exposed to sunlight in the presence of water a crystalline compound is formed which has the composition C10 H18 O2, and is named by Armstrong sobrerol. Pinene in contact with water gradually combines with it, forming a crystalline hydrate, terpene hydrate, C10 H16 3 H2 O, which is soluble in alcohol, insoluble in turpentine, slightly soluble in cold water, a little more freely in hot water, and sparingly soluble in ether, chloroform and carbon bisulphide.

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There are two varieties of pinene, which differ from one another simply in their action on a ray of polarised light. One variety, that in French turpentine, turns the ray to the left, and is distinguished as lævo-pinene, the other is found in American turpentine, and turns the ray to the right, and is named dextropinene. The air-oxidation and other products from the two terpenes differ from one another in the same manner. A mixture of the two pinenes, in equal proportions, would have no action on polarised light, and gives rise to inactive oxidation products. American turpentine contains both pinenes, the dextro variety predominating.

Sylvestrene is the characteristic terpene of Russian and Swedish turpentine, derived from the Scotch pine, Pinus sylvestris. It is a colourless, or water-white limpid liquid, having a specific gravity of 0.846 at 20° C.; it boils at 175° C. It has a dextrorotatory action on polarised light; the lævo-rotatory and inactive varieties are not known. Dry hydrochloric acid gas, when passed through sylvestrene, forms an hydrochloride, C10H16 H C1, which is liquid. In this respect this terpene differs from pinene; it is also more easily oxidised when exposed to air and light.

The other terpenes are of no practical importance to the painter. Commercial French and American turpentine is a water-white, limpid liquid, with a peculiar and characteristic odour that distinguishes it from all other bodies. The specific gravity ranges from 0.864 to 0.870, but usually is about 0.867. French turpentine is a little more uniform than American turpentine in this respect. It begins to boil at from 156° to 160° C., and is completely distilled at 170° C. If the sample be fresh, there is little or no residue left behind, but old samples generally leave a slight residue of resinous matter, which in any case does not amount to more than 1 per cent. of the turpentine.

Turpentine is readily combustible, burning with a smoky flame, a peculiar and characteristic odour being evolved. The flashing point of ordinary turpentine is 36° to 38° C. (97° to 100° F.).

Turpentine is readily miscible with ether, carbon bisulphide, alcohol, benzene, petroleum spirit, but it is insoluble in water. It is a good solvent for oils, fats, resins, &c.

On exposure to the air in bulk, turpentine absorbs oxygen slowly from the atmosphere, becoming thick and viscid or fatty in appearance. A prolonged exposure causes the turpentine to become resinous, part of the turpentine volatilising during the exposure. In thin layers, such as would be formed when turpentine is spread over a surface with a brush, a condition of affairs which occurs in painting, there is less oxidation, as a larger proportion of the turpentine volatilises away, and the oxidation of the residue is more complete, so that a hard resinous product is the result. This property distinguishes turpentine from all the other spirituous liquids used by the painter and varnish maker. These evaporate completely away, and consequently leave no residue behind which can act as a binding agent for the pigment or colouring matter of the paint; whereas, the resin left when turpentine is used, acts as a binding agent, and fixes or fastens the pigment of the paint on the surface over which it is spread. American has greater absorbing powers for oxygen than French turpentine.

Exposed to the air in contact with water, turpentine forms a solid crystalline product, having the composition C10 H18 O This has been named sobrerol; the melting point is 150° C. for the active variety, and 130.5° to 131° C. for the inactive variety. The crystals belong to the rhombic system, the inactive variety being of a different form to the active varieties. They are somewhat soft and flexible, and are soluble in alcohol. When repeatedly distilled with strong sulphuric acid, turpen

tine becomes polymerised. Generally two bodies are formed. One of these has been named terebene, which has the same formula (C10 H16) as turpentine, and, when pure, boils at 160° C. The other body has been named colophene, has the formula C20 H 32 and boils at 300°C. It constitutes the main product of the reaction. This property of polymerisation, which is essentially a conversion from a spirit boiling at a low temperature into a spirit boiling at a high temperature, distinguishes turpentine from any of its substitutes.

Nitric acid acts very energetically on turpentine, the result varying with the strength of the acid used. If strong enough, the turpentine may take fire; in any case, various oxidation products are obtained.

Chlorine, bromine, and iodine act with great energy on turpentine; great care must be taken in bringing these bodies into contact with one another or explosions may occur.

Turpentine has a strong action on polarised light, a property which distinguishes it from benzene, petroleum spirit, and rosin spirit. French turpentine rotates the ray to the left, its specific value being 30, and is fairly constant, showing that French turpentine has a very uniform composition; this fact is also shown by its regular specific gravity and by its steady distillation temperature. The specific rotation of the pure terpene, terebenthene, is 40. American turpentine rotates the ray to the right, but the variation of the value in different samples is very great; ordinary commercial samples give specific values ranging from + 8 to 16; the pure terpene has a specific rotation of + 21.5. It is quite possible that American turpentine contains a small quantity of a lavo-terpene, the quantity of which varies in amount and, consequently, the specific rotation must vary also. The air oxidation products (sobrerol) in their action on polarised light vary with the turpentine from which they are obtained; that from French turpentine rotates the ray to the left with a fairly uniform specific value, while that from American turpentine is rather variable and can be separated into two varieties, one with a + and the other with a specific rotation; while, by mixing the two in equal proportions, an inactive variety can be obtained. Burmese turpentine from Pinus Khasyana, which resembles French and American turpentine in its general properties, differs by having a strong and uniform + rotation.

Russian turpentine resembles American turpentine in many of its properties, such as solvent and soluble features, action of nitric acid, sulphuric acid, chlorine, &c. It is rather more