and fifth years they are increased by about 30 in. a year, so that they are about 12 ft. high by the end of the fifth year. The breadth of the incision remains as before, not exceeding 4 in.

As the incision extends upwards, the zinc gutter and the collecting-pot are also moved up above the hard inspissated part, so as to prevent evaporation of oil of turpentine and get as large a proportion of fluid resin (gemme) as possible, while reducing to a minimum the hard incrustations that have to be picked or scraped off. Every two to three weeks the gemme in the collecting-pots is emptied into a basket and taken to a resin-reservoir (barcous), consisting of the half of a barrel let into the ground and protected by a wooden cover. Very little of the hardened resin can by this method be hand-picked (galipot), as most of it forms a hard incrustation (barras), which has to be scraped off twice a year, in June and November. In packing French resin for the wholesale market, in barrels of 235 kilo., or about 4 cwt. each, the proportion of scraped resin must not exceed 18 per cent of the whole weight, or about 1 part barras to 5 parts gemme.

Fig. 285.

The trees are either tapped to death (gemmage à mort), or else merely to a slighter extent (gemmage à vie). The completely exhaustive process is only applied to trees that have in any case to be felled for one reason or another (e.g., thinnings, and fully mature trees); and as the object then is to obtain as much resin as possible, from 2 to 6 incisions are made simultaneously in the stem. The second and non-exhaustive process is applied to all trees which it is intended to tap for several years in succession; and in this case only one incision is made at a time. When this one groove has been worked for five years, and the incision is therefore about 12 ft. long, the tree is given a rest for several years, and a new incision is made parallel to the former one, and about 6-8 in. from it. This new groove is then tapped for five years, and a rest again allowed; and so on, till the whole bole is ribbed with the resinified and more or

less parallel grooves. Under this treatment the butt of the tree becomes much swollen and hypertrophied. Trees tapped to death are mostly sawn into sleepers, the small wood being exported to Britain as pit-props.

The yield in woods of 30-35 years old is on the average about 240 kilo. (or a little more than 1 barrel of 235 kilo., or 4 cwts., and containing about 50 gallons), while 40-70-year-old crops give 450 kilo. per hectare annually, which is equivalent to about 1.87 and 3.53 cwt. of crude resin per acre annually. On the average about 4 lb. (1 gallon about 10 lb.) is collected from each grooved incision, though the quantity of course varies with the size of the tree; and each man employed can work about 5000 grooves, and collect about 40 barrelsful (or about 2000 gallons, weighing about 180 cwt. or 9 tons) of crude resin during the course of the season from March to October.

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(2) The Austrian method of tapping the Black Pine, less economical than the above, consists in first making, about the middle of April, a deep cup-like incision into the butt of the stem about 1 ft. above the ground, in which the resin collects on trickling down. This incision (Grandel) generally extends about one-fourth to one-third round the stem (but sometimes more, up to a maximum of two-thirds of the girth), and to a depth of about 3 in. (Fig. 285). On each side of this a slanting cut is made above it, so that their downward ends point inwards, and form grooves directing the flow of the resin towards the cup-like hollow; and above these the bark is peeled and the sapwood of the last 2 to 4 years chipped away. It is useless to cut in

deeper, as no resin exudes from the heartwood. At first the blaze is only made a few inches high, but as it has to be freshened once a week, it gradually extends to 14-16 in. by the end of the first season; and in the following years it needs freshening every 4-5 days to prevent incrustation and stoppage of the exudation. Tapping is continued for about 8-12 years, the barked and blazed surface gradually increasing in height by about 15 in. a year, while the breadth remains the same from year to year.

The tapping season extends from spring to autumn, beginning in the second half of April and continuing till the beginning or middle of October. During the first year, while the blaze is still small, most of the resin flows (Rinnharz) into the cuplike incision, and comparatively little becomes incrusted on the blaze, and has to be scraped off (Scharrharz); but when the blaze becomes prolonged and the resin has farther to trickle down in reaching the Grandel, a good deal of oil of turpentine evaporates, and most of the resin incrusts, and has to be scraped off. To minimise this loss by evaporation, side-cuts are made at either side of the blaze, parallel to the two first cuts made above the cup, and chips of wood (Leitspäne) are inserted in them, in order to keep the flow of the resin as near the centre of the blaze as possible. Every fourteen days the resin is collected from the Grandel and stored in casks let into the ground, while the hard incrusted resin is scraped off with an iron in autumn.

Only one blaze is usually made on each stem, but large trees are sometimes tapped twice, the second blaze being made when the first has reached a height of 13-16 ft., so that only two narrow bands of bark then remain on the stem.

The yield of resin varies of course according to the size of the trees, the soil, situation, climate, &c., but is largest in quantity and best in quality in small trees from the fourth to sixth years of tapping, and in large trees during the seventh to ninth years; and most resin exudes about the end of June. The best out-turn is obtained when the blazes are refreshed during mild, soft weather, and when the freshly-cut surface is yellowish-red. Trees of 10-12 in. diameter yield on the average from 3 to 5 lb. of crude resin annually during the ten years' period of tapping, while those above 12 in. diameter give from 7 to 9 lb.; and in either case the proportion of hard resin (Scharrharz), worth only two-thirds of the price of the finer quality (Rinnharz), usually varies from about 40 to 60 per cent. The resin is rich in turpentine, 1 cwt. of crude resin distilling off 15-22 lb. weight of oil of turpentine, and leaving about 67 lb. of rosin as residuum (see p. 615). Tapping makes the wood coarser and rougher, but improves its technical qualities.

(3) The German method of tapping Spruce, now only practised to a very slight extent, differs from the above methods owing to the resin incrusting soon in place of flowing. It consists in cutting two blazes into the sapwood in May or June on opposite sides of the stem to a height of 3-5 ft., and a breadth of 1-2 in., and ending in a point at the lower end, so as to prevent rain-water lodging. During the first year the blazes become incrusted with resin, which is scraped off in July of the following year; and every 2 to 3 years (or in some places every year) they are refreshed by their edges being pared at the sides during the summer, until at length only two narrow strips of bark remain on the stem. Sometimes a modification of this method obtains, where only two narrow blazes are made at first and tapped for two years; then two new blazes are opened and tapped for other two years; and so on till only narrow strips of bark are left uncut. The tapping of Spruce trees generally continues for 10 to 15 years, and the yield per tree averages about 1 lb. of resin annually, about two-thirds of which (Bruchharz) are scraped off the face of the blaze, and one-third is of coarse and poorer quality (Pickharz) cut from the edges.

(4) The Alpine method of tapping Larch differs from all three of the above ways, in that the resin is mainly obtained from the heartwood, and from the region

between heart- and sap-wood, where shakes in the tree get filled with resin. The tapping consists in boring in early spring an auger-hole of about 1-1 in. in diameter into the stem in a slightly upward slanting direction, about 1 ft. above the ground. This hole is bored right in to the centre of the tree, and is bunged up with a wooden plug. By autumn this hollow becomes filled with resin, which is then scooped out clean with a long, hollow, semi-cylindrical scoop (Räumer). The hole is then plugged up again, and the fresh resin collecting is removed annually for about 20 to 30 years. Sometimes, however, the bore-hole is left open for the first season and the exuding resin is collected in pots; and after the first autumn the hole is plugged up, and cleared out and left open again once every 2 to 6 years; but no new hole is bored into any tree already tapped. Trees are not tapped till they are at least 80 years old, and those with thick bark give most resin, although the quantity yielded depends to a great extent on whether or not any, or many, resinous clefts happen to be bored through.

The yield may therefore vary greatly, from about to 1 lb. per tree per annum, although large trees tapped with an open bore-hole can yield up to 64 lb. during the course of a year.

The resin collecting in stopped-up holes is of better quality, though less in quantity, than that allowed to flow out, which is dirtier, and contains less oil of turpentine. This practice does not deform the stem like the methods used with other trees, but it exhausts the tree considerably. Though small in quantity, Larch resin is of superior quality.

2. The crude Resin is almost entirely used for the distillation of oil of turpentine and rosin or colophony, only small quantities being employed medicinally (for ointments, bandages, &c.). When the oil of turpentine is entirely distilled off, the residuum is rosin or colophony; but when only part of the former is extracted, the viscous mass remaining is known commercially as common, crude turpentine.

Distillation may either take place primitively in small local works, or by a more careful and elaborate method at some central factory, the latter being the more thorough and economical way of working on any large scale.

In the primitive method the crude resin is put into a large copper kettle or boiler with a movable lid, and boiled over an open fire. When the resin melts, water is added to assist in dissolving the oil of turpentine, which is carried off along with the steam through a cooling-worm into a receiver shaped like a Florentine-flask, where the condensed vapour is collected and the oil separates and floats above the water. When the whole of the oil of turpentine obtainable in this rough fashion has been separated, the watered resin or "white pitch" remaining in the boiler still contains a considerable quantity of minute drops of water, and on cooling becomes a hard, dull, bright-yellow to syrup-brown mass, which is used for sizing paper and closing the pores of cask-staves (but not for making brewers' pitch, see p. 615). But this water must be got rid of entirely before marketable rosin or colophony is prepared, so the lid of the boiler is taken off and the contents boiled until they become transparent, when they are strained by being poured through a wire or straw sieve into boxes or casks for transport. Impurities, such as chips of wood and bits of bark, are thus easily got rid of, while heavier, earthy dirt sinks to the bottom of the boiler, and can be broken up, and re-boiled and purified when a sufficient quantity of it has been collected. As the contents of the boiler are heated very unequally, this primitive method produces only ordinary dark-brown rosin, more or less dulled and discoloured through the decomposition of part of the crude resin which sticks to the superheated parts of the boiler next the fire. And of course the yield of oil of turpentine, being only partial, is comparatively small.

The better method is to melt the crude resin and strain it through a sieve

before commencing distillation. The filtering vat is double-walled for steamheating, and contains a movable sieve; and it is connected with the distilling retort by a pipe, so that the filtered resin reaches this in a warm and fluid condition. The sheet-iron retort has both an outer casing for steam-heating, at about 180°-190° Fahr., and also a steam-pipe, so that steam can be turned directly into it; and the base is prolonged like a wine-funnel, so that the rosin can afterwards be run off easily and entirely. Distillation is best effected under diminished pressure, obtained by passing blasts of steam through the throttle of the pipe leading from the top of the retort to the condensing apparatus. The latter consists of coils of tubing, around which cold water is kept circulating; and on the oilcharged vapour being condensed and passed into the reservoir-tank, the lighter turpentine can easily be separated as it floats above the heavier water, and can be run off by an overflow pipe. And when all the oil of turpentine has been distilled off, the rosin or colophony is run off in a clear, pale yellow-brown stream by the pipe at the base of the retort, and strained through copper wire-gauze while still hot. From here it passes into a tank, from which it is run off into barrels containing about 7 cwt. each, or into moulds forming cakes of convenient size for packing in casks. By means of the partial vacuum which can thus be created as above described, the filtration of the crude resin and the filling of the retort can take place more easily and quickly, while the quantity of oil of turpentine is larger and its quality better, owing to distillation being effected at a lower temperature than is otherwise possible.

The yield of oil of turpentine and rosin varies greatly, according to the kind and quality of resin. But, on a rough average, crude resin in general gives (by weight) from 15 to 30 per cent of oil of turpentine and about 65 to 75 per cent of rosin or colophony, while from 5 to 10 per cent are due to impurities (bark- and wood-chips, earth, &c.) and loss in the process of distillation. Among the European Conifers habitually tapped for resin, that of Silver Fir and then that of Larch contains the largest percentage of turpentine, that of Maritime and Black Pines occupies an intermediate position, and that of Spruce contains least.

Products of Resin.-When crude resin is combined with metallic oxides, resinates are formed. Alkaline resinates are soluble in water, lather freely, and form resinous soap; and when this is made with any alkaline earth, it is much less soluble in water than ordinary fatty soaps.

Oil of turpentine consists of a mixture of hydrocarbons, and its chief component is a substance called pinen, having the chemical formula C10H16. It is insoluble in water, but dissolves in alcohol, æther, benzol, &c. In the crude product obtained by distillation over an open fire the turpentine also contains some of the products of the decomposition of the rosin, as well as resinous acids, &c. This can be refined and rectified, however, by mixing it with lime-water and re-distilling it by steam-heating; but even after re-distillation each kind of turpentine has its own peculiar properties. When fresh, oil of turpentine is a thin, colourless fluid with a very distinctive odour, which varies according to the kind of resin used in obtaining it, and with a sp. gr. of 0·85-0·88, and a boiling-point of 300°-330° Fahr., although it evaporates freely at any ordinary temperature. On giving off its essential oil it absorbs atmospheric oxygen, and forms a pungent aldehyde (C10H1603); and as oxidisation proceeds further, the oxygen is transformed into ozone, and the whole gradually turns into a solid, brittle, pale-yellow colophonous mass, having an acid reaction. Oxidisation takes place quickest when water is present. When oil of turpentine is combined with hydrochloric acid gas it forms a soft, kneadable mass (C10H16HCl) known as artificial camphor.-Oil of turpentine is a good solvent for many resins, wax, fats, caoutchouc, sulphur, and phosphorus, and it is largely employed in making varnish, in oil-painting, &c.