Source, Etc

Guaiacum resin is the resin obtained from the stem of Guaiacum officinale, Linne, or Guaiacum sanctum, Linne (N.O. Zygophylleoe). The bulk of the resin of commerce is produced in the following rather crude way from the trunk of the tree, the heartwood of which, as already stated (see 'Guaiacum Wood'), contains from 20 to 25 per cent, of resin: A log of the wood is supported in a horizontal position above the ground by two upright bars. Each end of the log is then set on fire, and, a large incision having been previously made in the middle, the melted resin runs out therefrom in considerable abundance (' Pharmacographia'); or one end of a log of wood is raised, and fire applied to it, when the melted resin will run out of a groove cut in the other end, and may be received in potsherds (block resin).

It is said that the resin may also be obtained in the form of tears by incisions made into the trunk, but it is more than doubtful whether the tear resin of commerce is so produced.

Description

Guaiacum resin is usually seen in large masses of dark colour, often more or less covered with a greenish powder. The resin breaks easily with a clean, glassy fracture, thin splinters viewed by transmitted light being transparent, and varying in colour from yellowish green to reddish brown. The powder is greyish, but becomes green by exposure to light and air. It has a slightly acrid taste, and, especially when warmed, a somewhat balsamic odour. It is freely soluble in alcohol, chloroform, and solution of caustic potash, incompletely in ether, but only slightly soluble in petroleum spirit, carbon disulphide, or benzene.

The resin in tears forms rounded masses, attaining 2 to 3 cm. in diameter, usually covered with a greenish powder, and exhibiting the characters already detailed.

The commercial drug is never completely soluble in alcohol. The residue, which in the case of tear resin is about 1.5 per cent., and in good samples of the lump averages about 7.5 per cent. (Evans, 1898; not over 10 per cent., B.P., 1914), may in exceptional cases amount to as much as 25 per cent. It consists chiefly of fragments of vegetable debris, gummy matter, etc.

Guaiacum resin is easily identified by its remarkable reaction with oxidising agents. This is best seen by dissolving a little of the resin in alcohol and adding a drop of dilute solution of ferric chloride; the liquid instantly assumes a deep blue colour which is destroyed by reducing agents, but restored by oxidising agents.

The student should observe

(a) The varying colour that the resin exhibits when viewed by transmitted light,

(b) The greenish powder with which it is often more or less covered,

(c) Its characteristic, though not powerful, odour and taste.

Constituents

Guaiacum resin consists chiefly of resin-acids and has approximately the following composition: -

α-Guaiaconic acid

70.00

per cent.

β-Guaiaconic acid

Guaiaretic acid ...

11.25

"

Guaiac-β-resin ...

1500

,,

Guaiacic acid, guaiac-yellow, vanillin, saponin, etc. ...

2.25

"

α-Guaiaconic acid is a colourless amorphous substance, probably a mixture, one constituent of which is changed by oxidising agents to deep blue guaiac-blue; sulphurous acid reduces this to a colourless substance, which may again be oxidised.

β-Guaiaconic acid is colourless and crystalline. Guaiaretic acid is light brown, amorphous, and insoluble in ether. Guaiac-β-resin is brown and amorphous, and appears to be chiefly a decomposition product of the guaiaconic acids; it contains the substance that yields guaiac-blue by oxidation.

Uses

The action of guaiacum is that of a local stimulant or, in large doses, irritant. It has been employed locally in the form of the lozenge, and has also been given in chronic gout and rheumatism.

Adulterants, Etc

Guaiacum resin is normally so cheap that it offers little inducement for adulteration. Colophony which has been mixed with it may readily be detected by shaking the freshly powdered resin with petroleum spirit and shaking the filtrate, which should be colourless, with 0.1 per cent, solution of cupric acetate; if colophony is present the petroleum spirit will assume a vivid green colour. The acid value is about 90, but the determination is unsatisfactory, as the end-reaction is indefinite. Guaiacum resin in other resins may generally be detected by the ferric chloride reaction.

Peruvian guaiacum is brownish and aromatic, and is used in perfumery; its botanical origin is unknown.