The greenish colour of certain pieces of manna was formerly attributed to the presence of copper, till Gmelin, on account of the fluorescence of the solution, ascribed it to Æsculin. It is in reality produced by a body much resembling æsculin, namely Fraxin, C₁₆H₁₈O₁₀, occurring in the bark of the manna-ash and of the common ash, and together with æsculin, in that of the horse-chestnut. Fraxin crystallizes in colourless prisms, easily soluble in hot water and in alcohol, and having a faintly astringent and bitter taste. By dilute acids, it is resolved into Fraxetin, C₁₀H₈O₃, and Glucose, C₆H₁₂O₆. The presence of fraxin in manna, especially in the inferior sorts, is made apparent by the faint fluorescence of the alcoholic manna solution. The smallest fragment of the bark of the ash or the manna-ash immersed in water displays the same fluorescence.
Commerce—The exports of manna from Sicily[1512] (chiefly from Palermo) have been as follows:—
| 1869 | 1870 | 187 |
| 2546 cwt., | 1564 cwt., | 3038 cwt., |
| val. £15,972. | val. £10,220. | val. £19,528. |
About half the quantity is sent to France. Italian commercial statistics[1513] represent the export of manna in 1870 thus:—in canelli 58,691 kilo. (1155 cwt.), in sorte 186,664 kilo. (3676 cwt.). The United Kingdom imported in the year 1870, 230 cwt. of manna, valued at £4447.[1514]
In 1877 the exports of “canelli” from Messina were 4273 kilogrammes, and of the drug “in sorte” 52,874 kilogr.; total value, 127,145 lire.
Adulteration—It can hardly be said that manna is subject to adulteration, though attempts to introduce a spurious manna made of glucose have been recorded. But considerable skill and ingenuity have been expended in converting the inferior sorts of manna into what has the aspect of fine natural Flake Manna, the manufacturers admitting however the factitiousness of their product. The artificial Flake Manna has the closest superficial resemblance to very fine pieces of the natural drug, but differs in its more uniform colour, and in being uncontaminated with the slight impurities, from which natural manna is never wholly free. It differs also in that when broken, no crystals of mannite are to be seen in the interstices of the pieces, and it wants the peculiar odour and slightly bitter flavour of natural manna. If one part of it is boiled with four of alcohol (0·838), a viscid honey-like residue will be obtained, whereas natural manna leaves undissolved a hard substance. Histed[1515] found it to afford about 40 per cent. of mannite, while fine manna similarly treated yielded 70 per cent.
Uses—A gentle laxative, much less frequently employed in this country than formerly, but still largely consumed in South America. Mannite, which possesses similar properties, is often prescribed in Italy.
Other sorts of Manna.
Various plants besides Fraxinus afford, under certain conditions, saccharine exudations, some of which constituted the Oriental Manna used in Europe in early times. So far as is known, they differ from officinal manna in containing no mannite.
Alhagi Manna; Turanjabín (Arabic); is afforded by Alhagi Camelorum Fisch. (Hedysarum Alhagi Pallas, non L.), a small spiny plant of the order Leguminosæ found in Persia, Afghanistan and Beluchistan. It had already been noticed by Isztachri.[1516] Excellent specimens of the manna, kindly obtained for us in the north-west of India by Dr. E. Burton Brown and Mr. T. W. H. Tolbort, show it as a substance in little roundish, hard, dry tears, varying from the size of a mustard seed to that of a hemp seed, of a light brown colour, agreeable saccharine taste, and senna-like smell. The leaflets, spines and pods of the plant, mixed with the grains of this manna, are characteristic and easily recognizable.