In the middle of the last century some Burgundy pitch was produced, according to Duhamel,[2309] in the present canton of Neuchâtel, but no such branch of industry is now pursued there, at least on a large scale. On the other hand, in the districts of Moutier and Delémont in the Bernese Jura this resin is still collected, though it is not known as Burgundy Pitch, but is termed simply Poix blanche (White Pitch). The surveyor of the forests of this district, which is one of the richest in Pinus Abies, has informed one of us that from 790 to 850 quintals are collected and exported to Basle, Zürich, Aarau and Vaud. The pitch is worth in loco (1868) 100 to 110 francs (£4 to £4 8s.) the bosse of 6 quintals. The quantities collected in other parts of Switzerland are even less considerable.
Description—Pure Burgundy pitch, of which we have numerous authentic specimens, is a rather opaque, yellowish-brown substance, hard and brittle when cold, yet gradually taking the form of the vessel in which it is kept. It is strongly adhesive, breaks with a clear conchoidal fracture, and has a very agreeable, aromatic odour, especially when heated. It does not exhibit a crystalline structure, although, as we have frequently observed, the resin on the stem of the tree is distinctly crystalline.
Burgundy pitch is readily soluble in glacial acetic acid, acetone, absolute alcohol, and even in alcohol of 75 per cent. (sp. gr. 0·860), yet its solubility in these liquids is considerably altered by the presence of water or essential oil; and still more by the formation of abietic acid in the resin itself. The same influences also affect the melting point.
The crude resin of Pinus Abies,[2310] deprived of essential oil and dissolved in one part of absolute alcohol, was found to deviate a ray of polarized light 3° to the left, in a column of 50 mm.; the essential oil deviated 8·5° to the same direction. The oil contains a small amount of an oxygenated oil. After treatment with sodium the oil which remains does not form a solid compound if saturated with hydrochloric acid.
Chemical Composition—The investigations of Maly mentioned at [p. 607] afford a satisfactory elucidation of the chemical properties of the pinic resinous exudations. They all, according to that chemist, are mixtures of the same amorphous resin, C₄₄H₆₂O₄, with essential oils of the composition C₁₀H₁₆. These terebinthinous juices are collected and sold either in their natural state as turpentine, or deprived more or less completely of their volatile oil, in which condition they are represented by Burgundy Pitch, and finally by rosin or colophony.
The turpentines flowing down the stems of the trees gradually lose their transparency if allowed to dry slowly in the air, becoming at the same time harder and somewhat granular. This alteration is due to the incorporation of water, which at last is not only mixed with the components of the resinous juice, but to some extent combines chemically with the resin so as to transform it into a crystalline body having the characters of an acid. The fact is easily observed if clear drops of the turpentine of Pinus silvestris, P. Abies or P. Picea are collected in vials and kept perfectly dry. Thus treated these turpentines remain transparent, but the addition of water causes after a short time the formation of microscopic crystals of abietic acid, rendering them more or less opaque.
If turpentines are collected before they lose their essential oil by evaporation and oxidation, and before they have become crystalline, they can be retained perfectly transparent by distilling off the volatile oil without water. The distillation being most commonly carried on with water, the remaining resin is opaque.
Maly is of opinion that the same amorphous resin occurs in all the Coniferæ, and that it yields by hydration the same acid, namely Abietic, which has been described by former chemists as Pinic, Silvic, and Pimaric acids, all of which indeed are admitted to have the same composition. We must however remember that several sorts of turpentine, as Canada Balsam, appear incapable, according to our experiments, of yielding any crystalline resinoid compound whatever; and that their amorphous resin being but partially soluble is certainly not a homogeneous substance.
The crystals as formed naturally in the common turpentines do not exhibit precisely the same forms as those obtained artificially when the resins are agitated with warm diluted alcohol, as in the preparation of abietic acid. As to Pimaric Acid, we have prepared it in quantity from galipot, the resin of Pinus Pinaster, but have always found its crystalline character entirely different from that of abietic acid.[2311]
We are inclined, therefore, to think that the composition of the resins of Coniferæ is not so uniform as Maly suggests. The remarkable variety of their essential oils is a fact which seems in favour of our view.