Water disintegrates myrrh, forming a light brown emulsion, which viewed under the microscope appears made up of colourless drops, among which are granules of yellow resin. Alcohol dissolves the resin of myrrh, leaving angular non-crystalline particles of gum[574] and fragments of bark.
Chemical Composition—Myrrh is a mixture, in very varying proportions, of resin, mucilaginous matters, and essential oil. A fine specimen of myrrh from the Somali coast, with which Captain Hunter, in 1877, kindly presented one of us, yielded 27 per cent. of resin. The undissolved portion is partly soluble in water.
The resin dissolves completely in chloroform or alcohol, and the colour of the latter solution is but slightly darkened by perchloride of iron. It is but partially soluble in alkalis or in bisulphide of carbon. Brückner (1867) found this portion to yield 75·6 per cent. of carbon and 9·5 of hydrogen. The resin which the bisulphide refuses to dissolve, is freely soluble in ether. It contains only 57·4 per cent. of carbon. The resin of myrrh to which, when moistened with alcohol, a small quantity of concentrated nitric or hydrochloric acid is added, assumes a violet hue, but far less brilliant than that displayed by resin of galbanum when treated in a similar manner. But a most intensely violet liquid may be obtained by adding bromine to the resin dissolved in bisulphide of carbon. If the resin of myrrh as afforded by alcohol is warmed with petroleum (boiling at 70° C.), only a small amount of resin is dissolved. This liquid becomes turbid if vapours of bromine are added; a violet flocculent matter deposits, whereas the just above-mentioned solution in the bisulphide continues clear on addition of bromine.
The resin of myrrh is not capable of affording umbelliferone like that of galbanum. By melting it with potash, pyrocatechin and protocatechuic acid are produced in small amount.
Myrrh yields on distillation a volatile oil which in operating on 25 lb. of the drug, we obtained to the extent of ¾ per cent.[575] It is a yellowish, rather viscid liquid, neutral to litmus, having a powerful odour of myrrh and sp. gr. 0·988 at 13° C.[576] In a column 50 mm. long, it deviates a ray of light 30·1° to the left. By submitting it to distillation, we obtained before the oil boiled, a few drops of a strongly acid liquid having the smell of formic acid. Neutralized with ammonia, this liquid produced in solution of mercurous nitrate a whitish precipitate which speedily darkened, thus indicating formic acid, which is developed in the oil. Old myrrh is in fact said to yield an acid distillate. The oil begins to boil at about 266° C., and chiefly distills over between 270° and 290°.
On combustion in the usual way it afforded carbon 84·70, hydrogen 9·98. Having been again rectified in a current of dry carbonic acid, it had a boiling point of 262-263° C., and now afforded[577] carbon 84·70, hydrogen 10·26, which would nearly answer to the formula C₂₂H₃₂O. The results of Ruickholdt’s analysis (1845) of essential oil of myrrh assign it the formula C₁₀H₁₄O, which is widely different from that indicated by our experiments.
The oil which we rectified displays a faintly greenish hue; it is miscible in every proportion with bisulphide of carbon, the solution exhibiting at first no peculiar coloration when a drop of nitric or sulphuric acid is added. Yet the mixture to which nitric acid (1·20) has been added, assumes after an hour or two a fine violet hue which is very persistent, enduring even if the liquid is allowed to dry up in a large capsule. If to the crude oil dissolved in bisulphide of carbon bromine be added, a violet hue is produced; and if the solution is allowed to evaporate, and the residue diluted with spirit of wine, it assumes a fine blue which disappears on addition of an alkali. The oil is not much altered by boiling with alcoholic potash, nor does it combine with alkaline bisulphites.
The Bitter principle of myrrh is contained in the resin as extracted by alcohol. By exhausting the resin with warm water an acid brown solution is obtained, from which a dark, viscid, neutral mass separates if the liquid is concentrated; it is contaminated with a large amount of inorganic matter, from which it may be purified by means of ether. Yet the latter affords also but an amorphous, somewhat brittle brown substance, softening at 80°-90° C. This bitter principle reminds us of that mentioned in our article Elemi, page 151; it is but sparingly soluble in water; the yellowish solution is intensely bitter. The bitter principle of myrrh appears to be a glucoside. We have not succeeded in preparing it in a more satisfactory state.
Commerce—Myrrh is chiefly shipped by way of Berbera to Aden, and thence either to Europe or to Bombay. The exports of Aden in the fiscal year 1875 to 1876 were 1439 cwt.; one-half of which went to Bombay, one third to the United Kingdom.[578]
The bags or bales which contain the myrrh are opened in Bombay, and the drug is sorted. The better portion goes to Europe, the refuse to China, where it is probably used as an incense.[579]