This section is from the book "A Text Book Of Materia Medica, Being An Account Of The More Important Crude Drugs Of Vegetable And Animal Origin", by Henry G. Greenish. Also available from Amazon: A Text Book of Materia Medica : Being an Account of the More Important Crude Drugs of Vegetable and Animal Origin.
Most Coniferous trees contain in the wood a branching system of schizogenous secretion ducts filled with a viscid oleo-resin, which is exuded when the ducts are punctured. The amount thus yielded is, however, small. Very much larger quantities, practically the entire yield, are obtained by hacking the bark of the tree. In the new wood produced by the cambium immediately after such injury large numbers of oleo-resin ducts are formed, from which abundant oleo resin is poured out over the wound; after a time this formation of ducts and discharge of oleo-resin diminishes, and eventually ceases, but may be continued by repeating the injury which caused their production. The flow may therefore be continued for some considerable time. Hence the oleo-resin is not a normal (' physiological') but an abnormal ('pathological') product.
The term 'common' turpentine is practically restricted to the oleo-resin obtained in America, as the English market is almost exclusively supplied from that source. The bulk is obtained from Pinus palustris, Miller, the long-leaf pine, but P. Toeda, Linne, the loblolly pine, P. echinata, Miller, the short-leaf pine, and P. cubensis, Grisebach, the Cuban pine, all yield a considerable quantity. These trees, especially the long-leaf pine, form extensive forests in the southern and south-eastern United States, extending from Texas to North Carolina.
The oleo-resin is collected in the following manner:
In the winter, when no oleo-resin flows, cavities are cut in the trunk of the tree near the base; they slope inwards and downwards, and are destined to receive the turpentine. In the spring triangular incisions are made above the cavity or ' box,' the bark and part of the young wood being removed. The turpentine soon rapidly exudes and collects in the box, from which it is removed by a dipper. After eight or ten days the flow diminishes, but may be increased by cutting a strip of bark above the triangular incision; this process of hacking is repeated until the autumn, when the flow of turpentine gradually ceases. The last portions that are slowly exuded partially dry before they reach the box, and form a white incrustation on the hacked surface. This incrustation is removed and forms the drug known in America as 'scrape,' and in England as ' gum thus ' or ' American ' or ' common ' frankincense.
The crude turpentine is removed by a dipper from the boxes to barrels for transportation to the stills. These are of copper, and set in brick furnaces. Water is added and the whole warmed, any chips of wood, etc, that float to the top being skimmed off. The head is then luted on, and the heat increased. At first, water and oil of turpentine distil over, subsequently oil of turpentine alone. Water is occasionally added to prevent the resin from charring. After the distillation has been stopped the melted resin is run through wire strainers into barrels.
The finest resin is that obtained from the tree in the first year, when the crude turpentine yields about 80 per cent, of it. After that the proportion of oil of turpentine in the oleo-resin gradually diminishes, whilst that of the resin increases, but the latter become darker and darker in colour. Tschirch has shown that the yield of turpentine is greatly increased if the trees are wounded before the spring.
So enormous is this industry in the United States that it is computed that at least 800,000 acres of virgin forest are newly invaded annually to supply the turpentine stills in operation.
The resin thus obtained should form pale amber-coloured, transparent, glassy masses, very brittle and easily powdered. It is rather heavier than water, the specific gravity varying from 1 .070 to 1.085 (Dieterich). It has a faint terebinthinate odour and taste. At about 80° it softens, but it does not completely melt until the temperature exceeds 100°. It is soluble in alcohol, ether, and chloroform, and leaves when incinerated but little ash. Freshly powdered colophony is almost entirely soluble in petroleum spirit, but becomes much less soluble by long keeping. A thin film of the resin increases in weight by exposure to the air, a change probably due to oxidation.
Fig. 240. - Transverse section through the wood of Pinus maritima, showing an oleo-resin duct, c. Magnified. (Tschirch).
According to Tschirch and Studer (1903) American colophony has the following approximate composition:
Volatile oil .
The abietic acids are unstable crystalline isomeric acids to which the formula C20H18O2 is assigned.
The α- and β-acids are removed from an ethereal solution of the resin by shaking with solution of ammonium carbonate; the -acid by subsequent shaking with sodium carbonate solution, the resene remaining in the ethereal liquid. The acid value1 of colophony varies from about 136 to 180 and the saponification value from 157 to 200. Although the saponification value is uniformly higher than the acid value, the resin is nevertheless free from esters.
Colophony may be identified by its high acid value and by the following reactions: 0.1 gramme dissolved in 10 c.c. of acetic anhydride and cooled assumes a bright wine-red colour on the cautious addition of sulphuric acid; 01 gramme warmed with 2 c.c. of methyl sulphate gives a rose or violet coloration; a solution of 0-1 gramme in petroleum spirit shaken with a 0.1 per cent, aqueous solution of cupric acetate is coloured bright emerald green.
Colophony has stimulant and diuretic properties. It is used chiefly as an ingredient of ointments and plasters.
Resin is obtainable in commerce in various grades ranging from ' water-white ' to nearly black. Opaque resin is made by melting common resin with water.
Bordeaux turpentine is obtained chiefly from P. maritima, Poiret, in the south-western departments of Landes and Gironde. A vertical incision is made through the bark and about 1 cm. deep into the wood and an earthen pot is fixed at the bottom, in which the turpentine is collected. The cut is gradually lengthened until it is about 3 metres long, then the opposite side of the tree, and finally the edges of the cicatrix of the first cut are incised, the tree remaining productive for many years. A product similar to ' scrape ' is also obtained; it is termed ' galipot.'
The resin consists of pimarinic, pimaric, and α- and β-pimarolic acids. The volatile oil is distinguished from American oil of turpentine by being strongly laevorotatory.
Venice turpentine is obtained from the larch, Larix europoea, de Candolle, in France and Southern Tyrol, by boring into the stem in the spring, and collecting the oleo-resin that exudes. , It is a yellowish, slightly turbid, viscid liquid, with bitter aromatic taste. The resinous portion consists chiefly of a- and β-larinolic acids. A factitious mixture of colophony and turpentine is commonly substituted for it.
1 The acid value is the number of milligrammes of potassium hydroxide necessary to neutralise the acids present in one gramme of the resin. It is determined by dissolving a weighed quantity of the resin in alcohol and titrating with alcoholic solution of potassium hydroxide, using phenolphthalein as indicator.
The saponification value is the number of milligrammes of potassium hydroxide necessary to neutralise the acids and also to saponify the esters present. It is determined by boiling a weighed quantity of the resin with an excess of alcoholic volumetric solution of potassium hydroxide and titrating back with sulphuric acid.
The ester value is the number of milligrammes of potassium hydroxide necessary to saponify the esters present. It is obtained by deducting the acid value from the saponification value.
Oil of turpentine is chiefly produced by the foregoing method, Lower grades are obtained by the steam-distillation of the wood, roots, stumps, sawdust, etc. (wood turpentine), and also as a byproduct in the manufacture of sulphite cellulose. For pharmaceutical use it is freed from resinous and other impurities by redistillation. A comparatively small amount of the commercial oil is imported from France. American oil is usually dextrorotatory, though it may be slightly laevorotatory. French is strongly la3vorotatory. It consists chiefly of d- and l-pinene. Specific gravity, 0.860 to 0.870; refractive index at 25°, 1.465 to 1.480. It should distil almost entirely between 156° and 180° leaving no appreciable residue. It may be adulterated with illuminating petroleum or with rosin oil.
Colophony distilled at 80° to 250° yields ' rosin spirit' which is colourless, insoluble in water and in alcohol; about one-half consists of hydrocarbons boiling below 120°. At about 300° the resin yields ' rosin oil' a viscous, colourless to dark brown oil consisting of a mixture of hydrocarbons of high boiling point together with abietic acid.