CHAPTER XI.

THE SWEETS WE EXTRACT.

THE MANNA AND MILK SUGARS.

Manna sugars; their sensible and chemical characters.—Manna of the ash; its composition and uses.-Occurrence of manna sugar in sea weeds.-Gum-tree manna. ---Other mannas.-Oak, larch, and cedar mannas.-Persian manna.-The alhagi and tamarisk mannas.-The manna of the Scriptures; trees supposed to produce it. The real manna not known.-Liquorice sugar.-Milk sugar.-Analogies in the composition of cane, grape, and milk sugar.-How the two former are produced from each other, from starch, and from humic acid.—What chemists understand by chemical reactions.-How a knowledge of these improves old and gives rise to new chemical arts.-Illustration in the manufacture of garancine, and the use of madder in dyeing.

III. THE MANNA SUGARS form a third class of sugars which are distinguished from the grape and cane sugars by three principal characters. First, by their chemical composition; second, by their inferior sweetness; and third, by their not fermenting when mingled with yeast. Of this class, also, there are several varieties.

1o. Manna of the ash.-Two species of ash, the Fraxinus ornus, and the F. rotundifolia, yield this species of sugar. The European supply is chiefly derived from Sicily and Calabria. The F. ornus, a small tree of twenty to

twenty-five feet high, is there cultivated in plantations for the purpose. In the months of July and August, when the production of leaves has ceased, the sap is drawn from the tree.

For this purpose, cross cuts, about two inches long (fig. 43), are made in the stem, beginning at the lower part near the soil. These are repeated every day in warm weather, extending them perpendicularly upwards along the one side of the tree, leaving the other to be cut in the following year. The sap flows from these incisions, and is sometimes collected in vessels and sometimes allowed to harden on the outside of the tree.

and speedily concretes Fraxinus ornus-The Manna Ash, and the mode in fine weather into the

manna of commerce. The quality of the manna varies with the age of the tree, and with the part of the stem (lower or higher) from which it flows, and with the period of the season in which it is extracted. From the upper incisions, from trees of middle age, and in the height of the season when the sap flows most freely, the flake manna, most esteemed in England, is obtained in largest quantity.

Manna-besides a variable proportion of gum, which in some varieties amounts to a third of its weight-contains two kinds of sugar. The larger proportion consists of a pe

culiar, colourless, beautifully crystalline sugar, to which the name of mannite is given. This forms from 30 to 60 per cent. of the whole manna, and is properly the manna sugar. Mixed with this there is from 5 to 10 per cent. of a sugar resembling that of the grape, and which ferments with yeast. Thus, the manna of commerce consists, on an average, of about

The large admixture of gum diminishes the sweetness of the manna, and renders it less useful as a substitute for cane

sugar.

When newly extracted, manna is found to be nutritious as well as agreeable to the taste; and a considerable quantity of it is used as food, especially in Calabria. As it becomes old, however, it acquires a mild laxative quality, which unfits it for use as a part of the ordinary diet. This latter quality recommends it for use as a medicinal agent, for which purpose it is exported to various parts of Europe. The quantity yearly imported into Great Britain amounts to about 11,000 lbs., nearly all of which comes from Sicily.

This medicinal quality does not reside in the mannite or true sugar of manna, but in the other matters with which it is contaminated. By itself, in the pure or refined state, this sugar has no appreciable medicinal action, and were it abundant and cheap, might be employed for ordinary sweetening purposes. It is less sweet than cane sugar, and for daily use is not likely ever to compete with the latter in the market.

It is a singular fact that this peculiar manna-sugar exists

COMPOSITION OF MANNA.

229

in many familiar sea-weeds. It gives their sweet taste to those which are collected for eating along various parts of our coast, and is found in smaller quantity in many which are not perceptibly sweet to the taste. The Laminaria saccharina, when quite dry, contains above 12 per cent., or one-eighth part of its weight, of mannite. When the plant is dried in the air, the sugar exudes, and forms a white incrustation on its leaves. The Halidrys siliquosa contains from 5 to 6 per cent., and even the common Fucus vesiculosus 1 or 2 per cent. (STENHOUSE.) No use is made of this sugar of sea-weeds, except in so far as it assists, in some cases, in making them eatable.

Mannite in small quantity may also be extracted from common celery, and from the root of the dandelion; and it can be formed artificially from cane sugar.

2°. Eucalyptus sugar, or gum-tree manna.-' -The genus Eucalyptus, or gum tree of the colonists (fig. 44), forms a distinguishing feature in the landscape and forest scenery of Australia and Van Diemen's land. At certain seasons of the year, a sweet substance exudes from the leaves of these trees, and dries in the sun. When the wind blows, so as to shake the trees, this Australian manna is sometimes seen to fall like a shower of snow. the true manna, this sweet sub

Like

Fig. 44.

stance contains a peculiar crystallisable sugar-different, however, in composition and in some of its properties from the mannite already described. Though it is said to be produced in considerable quantities, I have not learned that it is customary to collect it for use as a sweet, either in Van Diemen's land or in Australia.*

3o. Other mannas.-Other sweet substances also are obtained from plants, to which the name of manna has been given. Thus, oak manna exudes from the leaves of a species of oak common in Kurdistan, and known to botanists as the Quercus mannifera, or manna-bearing oak. Larch manna is a sweet substance, which, in some countries, is found upon the European larch (Larix Europea) about the month of June. Cedar manna occurs in small globules on the branches of the Pinus cedrus. It is brought from Mount Lebanon, where it sells as high as 20s. or 30s. an ounce. It is much esteemed in Syria as a remedy for affections of the chest. Persian manna, or Gen, called also Alhagi manna, and by the Arabs Tereng jabim, is obtained from the camel's thorn (Hedysarum alhagi, Linn.), a plant which is indigenous over a large portion of the East. It yields manna, however, only in Persia, Bokhara, Arabia, and Palestine. Extensive plains are in these countries covered with the alhagi, and it is of great importance as food for the camels, as well as for sheep and goats. From the wounds produced by the browsing of these animals the manna chiefly exudes. It is collected by the Arabs and caravans which cross the Desert, and is used as food. It is gathered by merely shaking the branches.

Tamarisk manna is obtained from the Tamarix mannifera, a tree which grows abundantly in the neighbourhood of Mount Sinai. The manna of the Old Testament is sup

See the Author's Lectures on Agricultural Chemistry and Geology, 2d edition, p. 181.