Turpentine may be regarded as resin held in solution in a volatile oil. It is produced by numerous pines and other trees; but varies considerably in value, some kinds being used chiefly for the manufacture of resin, as that of the pinaster for instance; while the turpentine obtained from the silver-fir simply requires straining to free it from accidental impurities, and render it fit to be used in the manufacture of clear varnishes.
Mastic and Chian turpentine are obtained from Pistacia lentiscus and P. terebinthus, but the quantity is inconsiderable when compared with that obtained from various pines. In Europe, common turpentine is extracted from the Scotch fir, Baltic spruce, larch, pinaster, and silver fir. In North America, from the loblolly pine (Pinus tœda) and the Georgian pine (Pinus australis).
Actual experiments are necessary to determine to what extent the pines of New Zealand can furnish a substitute for the turpentine of Europe and North America; but there can be little doubt that large quantities can be obtained from the kauri, rimu, kahikatea, and others, by incision of the outer bark in a similar manner to that practised in North Carolina and other Southern States.
In some countries the resinous matter obtained from the trunk, by excision, is collected in baskets, which are placed over earthenware jars, so as to allow the fluid portion to drain off, forming the common turpentine of commerce. The solid portion is boiled in order to purify it, when it becomes ordinary resin.
The process of extracting the turpentine from the pinaster has been already described under the head “Resin.” Turpentine obtained from this
source, however, is of inferior quality to that obtained from the Georgian pine, and until the diminution of the American supply, caused by the civil war in 1863, it was chiefly used for the manufacture of resin; but during the continuance of the struggle it was imported into Britain in large quantities, which gradually diminished as the yield of the American product again increased, until, at the present time, it forms only one-tenth of the entire quantity imported,—it is sold under the name of Bordeaux turpentine. In North Carolina, Georgia, and Alabama, turpentine is extracted from Pinus australis and Pinus tœda in large quantities. During the winter months small cavities, termed “boxes,” are cut in the trunk of the tree at about twelve inches above the ground. The boxes slope inwards, the bottom being from four to five inches below the lower-lip, and of sufficient width to hold from one and a half to three pints of fluid sap. From one to four boxes are made in a trunk, according to its size and diameter,—a trunk fifteen inches in diameter should have three boxes, each holding about a quart. The boxes are cut with a long narrow axe, and require from eight to ten minutes each to make.
In the month of March the flow of sap commences, and continues to the end of August. In the former month the bark and sap-wood are cut or hacked for a few inches above the box, which is gradually filled, the flow increasing in quantity as the weather becomes warmer, so that the box is filled in about two or three weeks. The surface of the box should be lightly chipped over once a week, and the bark hacked afresh, the wounded portion being slightly increased in height each time, until in the course of years it is carried fifteen feet or more above the box. The turpentine is removed as often as necessary, and the resin that has dried on the surface of the boxes is carefully scraped off, and often mixed with it.
If the process be carefully conducted, trees may be profitably treated in this manner for forty or fifty years. The first year's produce is always the most highly valued, and is called “Virgin dip.”
The resin scraped from the surface of the wound forms the common frankincense or “Gum Thus” of the druggists, and is the chief ingredient in the incense used in Roman Catholic places of worship, serving as a substitute for the expensive Olibanum, or true frankincense of Arabia.
Turpentine is obtained from the larch by boring augur holes in the trunk ¾ inch to 1 inch in diameter, taking care not to reach the centre of the tree. The holes are slightly inclined upward, and have a tube or small gutter tightly fitted into each, with a tin canister or small bucket suspended from the outer end to receive the turpentine. The buckets are examined every morning, and the turpentine removed.
A mature tree will yield from seven to eight pounds of turpentine yearly for forty or fifty years.
The turpentine is often found collected in small cavities in the larch, exactly as in the New Zealand “red pine.”
In some cases the cavities are closed with a plug, and the turpentine allowed to remain until it assumes a pasty condition, when it is removed with an iron spoon. The yield is, of course, greatly reduced, but the durability of the timber is preserved.
Turpentine from the larch was formerly known as “Venice turpentine.”
In some pines, as the silver fir, in which the wood is destitute of resin ducts, the turpentine is contained in small cavities formed beneath the bark.
In the months of July, August, and September it is collected by Italian peasants, who visit the alpine districts for that purpose. Each carries a small sharp-pointed tin cone or flask, with which he punctures the bladders in the bark and extracts the turpentine, which he pours into a tin bottle carried at his belt. The loftiest trees are ascended by the aid of climbing-irons, so that the work of collection is extremely laborious. The turpentine is strained to free it from fragments of bark, leaves, and other impurities, when it is ready for sale. It is known in the market as “Strasburg turpentine,” and formerly commanded a high price.
The barbarous plan of cutting boxes in the trees would not be adopted in New Zealand, at any rate when it is desired to continue the process of extraction for a lengthened period. Tin or zinc troughs or boxes could be readily fixed to the trunk, or even sunk in the ground at its base, and the turpentine conducted to them by grooves, or some other simple contrivance. In this way even the kauri might be made to yield a supply of turpentine for some years without material injury to its timber.
Of course where a clearing is about to be made, and it is not thought worth while to convert the timber, the object is simply to obtain the greatest yield in the shortest time; in this case incisions may be multiplied, and cavities deepened without taking ulterior results into consideration.
The amount of turpentine and resin which our native pines are capable of yielding, involves several points of direct interest to the botanist, as well as to the merchant and settler. I therefore venture to suggest to settlers in forest districts, and especially to the proprietors of kauri and kahikatea forests, the desirability of ascertaining the yield of the different species by actual experiment, which might be commenced at once. In any case the results would be of great value, and their publication would confer a boon upon the community. The rate of flow should be carefully noted, and the variations caused by changes in temperature observed. It would be ad-
visable to try different methods of extraction with the same kind of tree, giving the preference to those which cause the least injury to the timber.
The Westland pine appears to merit particular attention—in common with the red silver pine it would probably afford turpentine of special value for certain purposes, although the yield of either would, in all likelihood, be comparatively small.