In Cassia Barks of considerable thickness, the same arrangement of tissues is met with, but their strong development causes a certain dissimilarity. Thus the thick-walled cells are more and more separated one from another, so as to form only small groups. The same applies also to the liber-fibres, which in thick barks are surrounded by a parenchyme, loaded with considerable crystals of oxalate of calcium. The gum-ducts are not larger, but are more numerous in these barks, which swell considerably in cold water.
Chemical Composition—Cassia bark owes its aromatic properties to an essential oil, which, in a chemical point of view, agrees with that of Ceylon cinnamon. The flavour of cassia oil is somewhat less agreeable, and as it exists in the less valuable sorts of cassia, decidedly different in aroma from that of cinnamon. We find the sp. gr. of a Chinese cassia oil to be 1·066, and its rotatory power in a column 50 mm. long, only 0°·1 to the right, differing consequently in this respect from that of cinnamon oil ([p. 526]).
Oil of cassia sometimes deposits a stearoptene, which when purified is a colourless, inodorous substance, crystallizing in shining brittle prisms.[1967] We have never met with it.
If thin sections of cassia bark are moistened with a dilate solution of perchloride of iron, the contents of the parenchymatous part of the whole tissue assume a dingy brown colour; in the outer layers the starch granules even are coloured. Tannic matter is consequently one of the chief constituents of the bark; the very cell-walls are also imbued with it. A decoction of the bark is turned blackish-green by a persalt of iron.
If cassia bark (or Ceylon cinnamon) is exhausted by cold water, the clear liquid becomes turbid on addition of iodine; the same occurs if a concentrated solution of iodide of potassium is added. An abundant precipitate is produced by addition of iodine dissolved in the potassium salt. The colour of iodine then disappears. There is consequently a substance present which unites with iodine; and in fact, if to a decoction of cassia or cinnamon the said solution of iodine is added, it strikes a bright blue coloration, due to starch. But the colour quickly disappears, and becomes permanent only after much of the test has been added. We have not ascertained the nature of the substance that thus modifies the action of iodine: it can hardly be tannic matter, as we have found the reaction to be the same when we used bark that had been previously repeatedly treated with spirit of wine and then several times with boiling ether.
The mucilage contained in the gum-cells of the thinner quills of cassia is easily dissolved by cold water, and may be precipitated together with tannin by neutral acetate of lead, but not by alcohol. In the thicker barks it appears less soluble, merely swelling into a slimy jelly.
Commerce—Cassia lignea is exported from Canton in enormous and increasing quantities. The shipments which in 1864 amounted to 13,800 peculs, reached 40,600 in 1869,[1968] 61,220 in 1871, and 76,464 peculs (10,195,200 lb.) value £267,703, in 1872.[1969] In 1874 the exports were 54,268 peculs (1 pecul = 133⅓ lb.) and 58,313 peculs in 1878; from the other ports of China cassia is not shipped to any extent. England usually receives no more than about 1,000,000 lb. of cassia, of which only 40,000 lb. appear to be consumed in the country. Hamburg imports about 2,000,000 lb. annually immediately from China. Yet in 1878 the quantity imported into London was 26,744 peculs (3,500,000 lb.), that received at Hamburg 13,548 peculs.
Cassia lignea is exported in chests containing 2 peculs each.
Oil of cassia was shipped from the south of China to the United Kingdom, to the extent in 1869 of 47,517 lb.; in 1870, of 28,389 lb.[1970] Hamburg is also a very important place for this oil; in the official statistics of that port for 1875 the imports from China are stated to have amounted to 30,000 lb., besides 10,000 lb. imported from Great Britain; in 1876 Hamburg imported 5,900 lb. from China and 17,000 lb. from England.
Uses—The same as those of cinnamon.