The trees are tapped for five years in succession, when they are not touched for a few years, and then tapping commences again; when the tree has got somewhat exhausted, the final tapping takes place, and a large yield of resin obtained, but the tree is killed. It is felled, and another planted in its place.

The distillation of the crude resin is carried on in the plant shown in Fig. 63, which is a front view or section of, and Fig. 64, which is a side view or section of the plant. A is a boiler heated by means of a steam coil, or (as shown in the drawing) by means of a fire, the former method being preferable; in this, the crude resin is heated to a temperature of 96° 0. (194° F.), when it becomes liquid. The boiler is fitted with a movable cover to prevent the easy escape of turpentine and the entrance of dirt. When the resin is melted, it is run into the tank, B, through the pipe, a; the particles of woody tissue, dirt, &c., are deposited in this tank, as also in the boiler, A. From the tank, B, the melted resin is run into a tank, C, which holds the quantity usually treated at one time (about 66 gallons); this tank is, therefore, a measuring tank, from this it runs through the pipe, b, into the still, D, which has the form shown; into this passes a steam coil, by which steam from an ordinary steam boiler can be sent into the still. An opening near the bottom of the still (which is kept plugged during the time the turpentine is being distilled), permits of the rosin being run off. E is an ordinary worm condenser fitted into a tub through which cold water is continually passing; with this worm condenser the still is connected by means of a goose neck (shown in the drawing).

The crude resin is placed in the still, 66 gallons being the usual charge; it is then heated by fire until a temperature of 135° C. (275° F.), is attained; when a current of steam is passed into the still, turpentine begins to come over and to condense along with the water from the steam in the worm condenser, the condensed products passing into a suitable receptacle, in which the water gradually settles to the bottom, while the turpentine rises to the surface; the latter is skimmed off and run into other narrow-mouthed vessels, in which it is allowed to stand for several days, during which the remaining water and other impurities settle out. The yield of turpentine is rather more than one-fifth that of the crude resin employed.

When all the turpentine has been distilled over, the residue in the still is run first into a tank, F, and from thence into a revolving screen, G, through which it flows in a fairly clear condition free from dirt and grit of any kind. By this means,

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. Cimonene, found in the essential oils of various species of

4.

aurantiacea, 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 H, 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.

2

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, C10 H16 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.