The glycerins are colorless, syrupy liquids, readily soluble in water, and of high boiling point.

The first of the series, that derivable from methane, is unknown. Its formula, CH(OH),, would be too unstable to allow of its isolation, as a molecule of water would undoubtedly split off from the three OH groups here indicated as attached to the same carbon atom. Its ethyl ester, CH(OCH ̧), is, however, known under the name of orthoformic ether (see p. 586).

The second glycerin of the series corresponding to ethane is also unknown. Its formula, CH(OH),, also indicates that to one of the carbon atoms two OH groups would be attached, which gives us an unstable molecule. Its ethyl ester, CH(OCH), is also known under the name of otho-acetic ether.

Propenyl Glycerin, CH,(OH), (Glycerinum, U. S. P.), is the triatomic alcohol corresponding to propane, and has the structural formula, CH2OH-CHOH-CH2OH. It occurs abun

dantly in nature in combination with the so-called fatty acids as esters of these latter, making up the bulk of the vegetable and animal fats and oils (see p. 621).

It is also produced in the alcoholic fermentation of sugar, and hence is found in most alcoholic beverages. It is also present in the urine as glycerin-phosphoric acid, a decomposition product. of lecithin and protagon. It may be formed artificially by the action of water at 170° upon trichlorhydrin (trichlorpropane), C,H,Cl2.

Practically, it is always obtained by the decomposition of the fats in connection with the manufacture of soaps and stearic acid. This decomposition may be effected by the aid of water in the form of superheated steam, by alkalies and metallic oxides, or by heating with sulphuric acid. For a fuller account of these methods, see section on Fat Industries.

The pure glycerin is a thick, colorless liquid, of specific gravity 1.27. It solidifies at low temperatures to monoclinic crystals, which fuse at 20° C. It boils at 290°, but in its ordinary impure state cannot be distilled at ordinary pressures without decomposition. It is very hygroscopic, and mixes with water and alcohol in all proportions. It is insoluble in ether, chloroform, carbon disulphide, benzine, benzene, and fixed or volatile oils. It is an excellent solvent for a great range of substances, such as bromine and iodine, alkaline chlorides, fixed alkalies, some of the alkaline earths, as lime, and a number of neutral salts. It also is said to have antiseptic properties.

Both glycerin and its naturally occurring compounds, the fats, decompose when heated, with the production of acrid penetrating vapors of acrolein and similar products.

The present annual production of raw glycerin throughout the world amounts to 40,000 tons, of which 26,000 tons are obtained from the stearic acid manufacture and 14,000 tons from soap manufacture.

Butenyl Glycerins, CH(OH),.-Two isomeric compounds of this class have been obtained. The normal compound, CH,.CHOH.CHOH. CH2OH, is a sweet, syrupy liquid, boiling at 172°-175° under a pressure of 27 millimeters.

Amyl Glycerin, CH,(OH),, has also been obtained as a thick, syrupy liquid, of a sweet and aromatic taste.

Hexyl Glycerins, C ̧H11(OH),.-Three isomeric compounds of this formula have been obtained, all of which are thick liquids, which can only be distilled under reduced pressure.

2n-2

6. Tetratomic Alcohols. General formula, C„H2-2(OH),. -If four hydrogen atoms of a saturated hydrocarbon be replaced by four OH groups, we obtain a tetratomic alcohol, which corresponds to a tetracid base. While the four OH groups characteristic of these alcohols seem to require at least four carbon atoms in the molecule, and hence no stable tetratomic alcohols can be expected from methane, ethane, or propane, yet ethers from these lower hypothetical alcohols have been obtained. Thus, ortho-carbonic ether, C(OC2H), a liquid of ethereal odor, boiling at 159°, corresponds to an alcohol, C(OH)4.

Erythrite (or Phycite), CH(OH), occurs free in Protococcus vulgaris, and combined with orsellic acid as an ester (erythrin) in many lichens and algæ. It forms large quadratic crystals, easily soluble in water, difficultly soluble in alcohol, and insoluble in ether. They fuse at 112° and boil at 330°.

Pentaerythrite, CH(OH),, has been made artificially by the action of lime upon a mixture of formic and acetic aldehydes in aqueous solution :

3CH2O + C2H4O + H2 = CsH12O4.

It crystallizes in large prisms, melting at 250°-255°, and is only moderately soluble in water.

7. Pentatomic Alcohols. General formula, CH-3(OH)5. -Pentatomic alcohols have not been found in nature, and until very recently had not been obtained artificially. They have been

obtained, however, in several cases by the reduction of certain pentoses (see Carbohydrates).

Arabite, CH2OH-(CH.OH),-CH2OH, has been prepared by the reduction of arabinose, CH10O5, with the aid of sodium amalgam. It fuses at 102°, and has a lævo-rotatory power in aqueous solution on the addition of borax.

Xylite, CH12O,, has been prepared by a similar method from xylose, CH10Os. It has not as yet been obtained crystalline, and is optically inactive.

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12

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Rhamnite, CH105, prepared from rhamnose, CH12O, is a homologue of the foregoing. It fuses at 121°, and is rightrotatory in aqueous solution even without the addition of borax. 8. Hexatomic Alcohols. General formula, CH-4(OH). -Several alcohols of the formula C.H12O, have been found in nature, and have excited interest because of their close relation to one of the groups of carbohydrates or sugars. The nature of their relation and a method for the synthetic formation of them from these sugars have both been indicated in connection with the classic work of Emil Fischer on the Carbohydrates (see next page).

Mannite, CH2OH—(CHOH),—CH2OH, is found in many plants, as in the larch, in celery, in the leaves of Syringa vulgaris, in sugar-cane, in Agaricus integer (of the dry substance of which it forms 20 per cent.), in rye bread, and notably in the manna ash (Fraxinus ornus), the dried juice of which constitutes Manna, U. S. P.

Mannite crystallizes from water in thick rhombic prisms, or from alcohol in silky needles, melts at 165°-166°, is only moderately soluble in water, scarcely soluble in cold alcohol, and insoluble in ether. Its aqueous solution turns the plane of polarization very slightly to the left, but in the presence of borax and other salts it is strongly dextro-rotatory.

It has been obtained artificially by Fischer from both mannose and fructose (lævulose) by reduction with sodium amalgam in neutral or weakly acid solution; when produced from fructose, sorbite, an isomeric alcohol, always accompanies it. Mannite is also formed from some of the sugars in the processes of fermentation, as in the lactic acid fermentation, and in especially large amount in the mucous fermentation of cane sugar.

Fischer has shown that there are three mannites obtainable : the ordinary mannite is the dextro-rotatory variety, and is always obtained in the reduction of a-mannose; a lævo-rotatory mannite

is obtained by the reduction of l-mannose; and an inactive mannite is obtained from the inactive mannose. The three varieties, besides differing in their optical characters, differ slightly in their fusing points and in their crystalline forms.

Sorbite, CH(OH), is found in the berries of the mountain ash and in the fruit of the plum, cherry, apple, pear, etc. It crystallizes out of water in small, colorless needles, which contain water of crystallization. The anhydrous substance fuses at 110°III. It is slightly lævo-rotatory in simple aqueous solution, but in the presence of borax is dextro-rotatory. It has been prepared synthetically from dextrose, and represents the dextro variety of sorbite only, the lævo-sorbite having been also.

Dulcite (Melampyrite), C.H.(OH), is found in certain plants like the Melampyrum nemorosum, but more particularly in the manna from Madagascar. It crystallizes in monoclinic prisms, fuses at 188.5°, and is still more difficultly soluble in water than mannite. Dulcite is optically inactive and not capable of being resolved into active modifications.

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Rhamno-hexite, C,H10(OH), a homologue of the preceding, has been prepared from rhamno-hexose, C,HO. It crystallizes from hot alcohol in small, colorless prisms, melting at 173°, and is dextro-rotatory.

9. Heptatomic to Nonatomic Alcohols.-Starting with the group of sugars (hexoses) corresponding to the hexatomic alcohols, Emil Fischer has built up synthetically several alcohols of higher classes. Thus, the addition of hydrogen cyanide to a hexose will give what is termed a nitrile; this when saponified yields an acid with seven carbon atoms, which can be reduced by sodium amalgam in successive steps to a sugar and a heptatomic alcohol. We may illustrate this in the case of mannose:

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In this way an artificial alcohol, d-mannoheptite, C,H1807, was prepared by Fischer, and later its identity with the naturally occurring Perseite was established.

Perseite is found abundantly in the fruits and leaves of Laurus persea. It crystallizes from water in microscopical needles, melt

ing at 188°. Its aqueous solution alone is inactive, but on the addition of borax becomes strongly dextro-rotatory.

By analogous synthetical reactions to those given above, there has been obtained from mannoheptose an octatomic alcohol, d-mannoctite, CH10(OH). By the same method, starting from 8-glucose, there have been obtained the following synthetic alcohols : a-glucoheptite, C,H1O7, fusing at 127°-128°; a-glucooctite, CH180g, fusing at 141°; and a-glucononite, C.H2O, fusing at 194°.

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III. ETHERS, OR OXIDES OF THE HYDROCARBON RADICALS.

The ethers may also be considered as the anhydrides of the alcohols. Thus, 2C,H,. OH= (С„H ̧),O + H2O. It may be, however, that two different alcohols can thus be united by the loss of one molecule of water. The resulting ether will then contain two different hydrocarbon radicals united by oxygen. Such a compound would be a mixed oxide. We distinguish, therefore, between the two classes, and have simple ethers or oxides of a single radical, and mixed ethers or oxides of mixed radicals. In both these cases, however, the radicals are obtained directly from the hydrocarbons by the loss of one or more hydrogen atoms, and are the same as unite with hydroxyl to form the alcohols. These alcohols, it will be remembered, were spoken of as basic hydrates, so the oxides will be basic oxides. Compounds where a basic or alcohol radical is united by oxygen to an acid radical used to be known as compound ethers, but, as they are really ethereal salts, they have been given the name of esters, to mark the distinction and to separate them clearly from the basic oxides or ethers.

We may distinguish between the ethers of the monatomic alcohols and those of higher alcohols.

1. Ethers of the Monatomic Alcohols.-These may be formed in several ways. By heating the alcohols with sulphuric acid the ethers can readily be obtained. The reaction goes on in two stages, however, as illustrated in the case of ethyl ether: (a) C2H5OH + SO2(OH), SO2(OH).OC2H5 + H2O. (b) SO2(OH)OC2H5 + С2H¿.OH C2H5.OC2H5 + SO2(OH)2. In the first reaction a compound known as ethyl-sulphuric acid (see p. 616) is formed, which then reacts with a second molecule of alcohol to form ethyl oxide or ether, and sulphuric acid is regenerated. Another general method for ether formation is to treat the halogen derivatives of the hydrocarbons with a sodium