Several varieties of turmeric distinguished by the names of the countries or districts in which they are produced, are found in the English market: but although they present differences which are sufficiently appreciable to the eye of the experienced dealer, the characters of each sort are scarcely so marked or so constant as to be recognizable by mere verbal description. The principal sorts now in commerce are known as China, Madras, Bengal, Java, and Cochin. Of these the first-named is the most esteemed, but it is seldom to be met with in the European market.[2370]
Madras Turmeric is a fine sort in large, bold pieces. Sometimes packages of it contain exclusively round rhizomes, while others are made up entirely of the long or lateral.
Bengal Turmeric differs from the other varieties chiefly in its deeper tint, and hence is the sort preferred for dyeing purposes.
Java Turmeric presents no very distinctive features; it is dusted with its own powder, and does not show when broken a very brilliant colour. Judging by the low price at which it is quoted it is not in great esteem. It is the produce of Curcuma longa var. β. minor[2371] Hassk.
Microscopic Structure—The suberous coat is made up of 8 to 10 rows of tabular cells; the parenchyme of the middle cortical layer of large roundish polyhedral cells. Towards the centre the transverse section exhibits a coherent ring of fibro-vascular bundles representing a kind of medullary sheath. The parenchyme enclosed by this ring is traversed by scattered bundles of vessels, and in most of its cells contains starch in amorphous, angular, or roundish masses, which are so far disorganized that they no longer exhibit the usual appearance in polarized light, but are nevertheless turned blue by iodine. The starch has been reduced to this condition by scalding.
Resin likewise occurs in separate cells, forming dark yellowish-red particles. The entire tissue is penetrated with yellow colouring matter, and shows numerous drops of essential oil, which in the fresh rhizome is no doubt contained in peculiar cells.
Chemical Composition—The drug yielded us (1876) one per cent. of a yellow essential oil, which contains a portion boiling at 250° C., answering to the formula C₁₀H₁₄O; this liquid differs from carvol ([p. 306]) by being unable to combine with SH₂. The other constituents of curcuma oil boil at temperatures much above 250°; we found the crude oil and its different portions slightly dextrogyrate.
The aqueous extract of the drug tastes bitter, and is precipitated by tannic acid.
The colouring matter, Curcumin, C₁₀H₁₁₀O₃, may be obtained to the amount of ⅓ per cent. by depriving first the drug of fat and essential oil. The powder, after that treatment with bisulphide of carbon, is gradually exhausted, according to Daube (1871), with warm petroleum (boiling point 80°-90° C.). On cooling chiefly the last portions of petroleum deposit the crystalline curcumin. Its alcoholic solution is purified by mixing it cautiously with basic acetate of lead, not allowing the liquid to assume a decidedly acid reaction. The red precipitate thus formed is collected, washed with alcohol, immersed in water, and decomposed with sulphuretted hydrogen. From the dried mixture of sulphide of lead and curcumin the latter is lastly removed by boiling alcohol.
By Ivanow-Gajewsky (1873) the best produce of curcumin is stated to be obtained by washing an ethereal extract of turmeric with weak ammonia, dissolving the residue in boiling concentrated ammonia, and passing into the solution carbonic acid, by which the curcumin is precipitated in flakes.