SYNTHESIS OF ORGANIC COMPOUNDS.

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and sulphuretted hydrogen upon carbonic disulphide; and from olefiant gas he has procured alcohol. He has further, by heating carbon intensely by means of a voltaic arc, obtained synthetically the hydrocarbon acetylene (E,H,). The same chemist has also, conjointly with De Luca, converted the hydrocarbon tritylene into glycerin, and he has further shown that glycerin may be transformed into one variety of sugar.

Strecker succeeded a few years ago in obtaining taurin by synthesis; and as researches in this direction are multiplied, new methods of preparing bodies till lately obtainable only from the products of the living plant or animal are daily being devised; so that the number of organic products which can be formed synthetically is now very considerable.

CHAPTER II.

THE SACCHARINE OR AMYLACEOUS GROUP.-VARIETIES OF
FERMENTATION.

(1076) THE Compounds which belong to the group to which the following chapter is mainly devoted are among the most important and abundant constituents of plants. They all contain carbon in the proportion of 6 atoms, or some multiple of 6, in their molecule. One of the most remarkable features of their chemical composition is the circumstance that they all contain oxygen and hydrogen exactly in the proportions requisite to form water, and hence they have by some writers been spoken of as hydrates of carbon. This term, however, is by no means intended to signify that all the hydrogen and oxygen exist in them united in the form of water, but merely to indicate that the proportion of their components is such as might allow of their elements being so arranged. Owing to this peculiarity of composition, many of these bodies admit of being readily transformed one into the other by the addition or abstraction of the elements of water, and several of them are especially prone to undergo the changes produced by fermentations of various kinds. In the presence of dehydrating agents, the sugars, lignin, and many bodies of this class yield humus-like products. When submitted to oxidation by the action of nitric acid, most of them yield oxalic acid; and under the influence of a mixture of concentrated nitric and sulphuric acids, substitution compounds are obtained, in which a

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THE AMYLACEOUS OR SACCHARINE GRoup.

portion of their hydrogen is displaced by peroxide of nitrogen. The most remarkable of these substitution compounds is pyroxylin (gun-cotton), the peculiar inflammability and explosive character of which is well known; but all of the nitrous substitution products of this class partake more or less of the inflammable and explosive properties which are so signally exhibited by pyroxylin. The bodies of the saccharine group readily undergo oxidation, especially in the presence of uncombined alkalies, and reduce many metallic oxides, such as those of copper and silver.

The researches of Berthelot and others seem to have rendered it probable that the sugars, as well as mannite and the bodies allied to it, are polyatomic alcohols like glycerin (1238); for they possess the power of entering into combination with various acids, with elimination of water, in some cases yielding peculiar colligated acids, analogous to the tannic, and in others furnishing neutral bodies closely allied to the fats. Linnemann has also shown that certain sugars may by the action of sodium amalgam be combined with hydrogen and converted into mannite (1244).

In the present chapter the compounds mentioned in the following table will be described. In a few of the substances enumerated in the lower part of the table, the proportion of oxygen and hydrogen differs from that of the sugars and starches.

Amylaceous and Saccharine Group.

Certain of these substances are soluble in cold water, such as the sugars and the gums. Others, like starch, become dissolved in water by the aid of heat, or rather become diffused through the liquid, though the solution is of a very imperfect character; whilst a third variety, including cellulin or ligneous fibre, is quite insoluble in water, whether hot or cold.

With the exception of sorbin and inosin, all compounds which have the constitution of hydrates of carbon are convertible either by prolonged boiling with dilute sulphuric acid, or by digestion in the strong acid and boiling after subsequent dilution, into one of the forms of glucose-viz., dextrose, lævulose, or galactose. But neither of these three forms of sugar appears to be convertible into either of the others.

The action of acids on some of these bodies may be illustrated by the following formulæ (Kekulé, Org. Chemie, ii. p. 334) :—

By the effect of heat certain of these sugars lose water, and

become converted into other hydrates of carbon, which, by

boiling with acids, are reconverted into the original compounds;

22

(1077) SEVERAL varieties of sugar are known to the chemist; but they may all be referred to three principal forms, viz., cane sugar or sucrose, grape sugar or glucose, and milk sugar or lactose. The most important of these is the common sugar furnished by the sugar cane, hence termed cane sugar, related to which are some others of small importance, viz., trehalose, melezitose, and melitose, represented by the general formula (EЄ12H22011,H2Ð). The second variety is that to which milk owes its sweetness: it has never been met with excepting in the milk of animals, and hence it is termed milk sugar (Є12H2211,H2O). The third variety constitutes the hard granular sweet masses common in old dried fruits, such as raisins, figs, &c., when it is known as grape or starch sugar, the latter name being derived from a method of preparing it artificially by boiling starch with a dilute acid. Connected with this variety are fruit sugar (lævulose), malt sugar, and galactose, the product of dilute acids upon milk sugar, all of which may be represented by the general formula (EH12,н ̧‡). These different varieties of sugar agree in possessing a powerfully sweet taste. Each, when pure, has always a definite degree of sweetness, but there are great differences in the relative sweetness of the different varieties. A pound of cane sugar, for example, will produce a greater sweetening effect than a pound of fruit or inverted sugar; and at least two pounds and a half of starch sugar are required to produce a sweetening effect equal to that of one pound of the cane sugar; while a given weight of the sugar from milk possesses less sweetening power than an equal quantity even of starch sugar.

These varieties of sugar differ greatly in external appearance as well as in chemical characters; and they also differ in chemical composition. If quantities of the different kinds of sugar which

CANE SUGAR OR SUCROSE.

93

contain equal amounts of carbon be compared together, it will be found that they differ in the proportion in which the elements of water are present. Comparing together quantities of sugar which contain 12 atoms of carbon, the proportion of water in each variety will be as follows:

There are few plants from which sugar is absent, and to which, at some period of their growth it does not form an important article of nutriment.

or

(1078) 1. CANE SUGAR or Sucrose Sucrose (12H22O11=342 C12HO=171).—This variety of sugar is chiefly obtained from the sugar cane; but the sugar maple and the beetroot furnish a considerable quantity for the market; it is also contained in carrots and turnips, as well as in the pumpkin, the chestnut, the young shoots of the maize, the ripe sorgho grass, and a large number of tropical fruits.

Properties.-Cane sugar has a sp. gr. of 16. It is soluble in about one-third of its weight of cold water, producing the thick viscid liquid known as syrup. It is also somewhat soluble in dilute alcohol, especially when heated with this liquid. It is insoluble in ether, and nearly so in cold absolute alcohol. By the spontaneous evaporation of its aqueous solution, it is deposited in large four-sided oblique rhomboidal prisms, which are often hemihedral, and are terminated by dihedral summits: these crystals constitute sugar-candy, which is colourless or brown according as the syrup employed is more or less free from colour. Ordinary loaf sugar consists of a congeries of minute transparent crystals, and the dazzling whiteness of the purest specimens is produced by the numerous reflections and refractions which the rays of light experience within the mass, from the numberless crystals of which it is composed. When two pieces of loaf sugar are rubbed together, a pale violet phosphorescent light is emitted.

If a solution of sugar be long boiled, it acquires an acid reaction, generally becoming less viscid, and irrecoverably losing its property of crystallizing; this change is attended by the assimila