Purity. The presence of water is shown by the specific gravity (see Alcoholometry); the absence of other foreign matter by the following tests:—
1. Its colour and transparency is not affected by the addition of a little colourless oil of vitriol (Liebig), or by a solution of nitrate of silver, and subsequent exposure for some time to solar light (Vögel), unless either essential oil or organic matter be present, when it assumes a reddish tinge. 2. It should be neutral to test-papers, colourless, leave no residue on evaporation, and be miscible, in all proportions, with water and with ether. 3. Its boiling point should never be less than 170° Fahr.; a lower temperature suggests the presence of wood spirits, or acetone, or one of the ethers. To detect wood spirit (wood naphtha) see Nessler’s Test. For the reverse of this adulteration—the evasion of the duty by the introduction of spirit, under the disguise of naphtha, turpentine, &c.—see those articles.
4. The presence of water in alcohol may be detected, not only by the sp. gr., but also by white anhydrous sulphate of copper burning blue when dropped into it. 5. Potassium placed on alcohol does not take fire, unless a considerable per-centage of water be present.
Tests, &c. 1. It may generally be recognised by its volatility, inflammability, odour, taste, miscibility with water, power of dissolving camphor and resins, and other qualities already described. 2. If a few fibres of asbestos be ‘moistened’ with a saturated solution of bichromate of potash in oil of vitriol, and exposed to the smallest possible portion of hot alcohol vapour, it is almost instantly turned green, owing to the formation of oxide of chromium. In practice, the asbestos may be inserted in the neck of a retort, or even of a bulbed glass-tube containing a few drops of the suspected solution, when the effect occurs as soon as distillation commences. Ether and pyroxylic spirit produce a nearly similar result; but the ‘first’ of these is distinguished from alcohol by its not being miscible with water in all proportions; and the ‘other’ by Nessler’s Test; whilst both may be readily distinguished by their peculiar and characteristic odour. 3. Dissolve 3 pts. crystallised carbonate of soda in 10 pts. water. To this solution add 1 pt. of liquid to be tested, and heat to about 160° Fahr. Lastly, add iodine in small pieces, till it has entirely dissolved, and the liquid has become colourless. If alcohol be present, iodoform will make its appearance on cooling, and sink to the bottom in the form of a yellow powder. As a similar result is obtained with wood spirit, this must be proved to be absent before applying this test.
The only reliable method of proving that a sample is ethylic alcohol is the production of ether, by acting on the suspected liquid with sulphuric acid. See Ether.
Uses. In the arts, alcohol is used by the varnish-maker to dissolve resins; by the perfumer, to extract the odour of plants, and dissolve essential oils, soaps, and other similar substances; by the pharmaceutist, to prepare tinctures and other valuable medicinals; by the instrument-maker, to fill the bulbs of thermometers required to measure extreme degrees of cold; by the photographer, in the preparation of collodion; by the chemist, in analysis, and in the manufacture of numerous preparations; by the anatomist and naturalist, as an antiseptic; and by the physician, for various purposes and applications as a remedy. It is also frequently burnt in lamps, and in parts of the world where it is inexpensive, it is employed in the manufacture of vinegar. Its uses, when dilute, as in the ‘spirituous liquors’ of commerce, are well known. In medicine, it is employed both concentrated (‘alcohol,’ ‘rectified spirit’) and dilute (‘proof spirit,’ ‘brandy,’ ‘gin,’ &c.), as a caustic, irritant, stimulant, tonic, &c. It has also been used in a multitude of other cases, and has been applied to an almost infinite variety of other purposes.
Gen. commentary. The selection of any one of the processes given above for the preparation of alcohol must greatly depend on the convenience or position of the operator. Chloride of calcium, and quick-lime, from their powerful affinity for water, and easy application, are the hygrometric substances most generally employed; but the processes involving the use of the other substances and methods already noticed, have all of them advantages under particular circumstances. Gay-Lussac has recommended the use of caustic baryta instead of lime; and others have employed dry alumina, as an absorbent of the water prior to distillation. Common proof spirit may be concentrated until its sp. gr. falls to about 0·825, by simple distillation in a water bath; at which sp. gr. it contains only about 11% of water, by weight, and is then nearly as volatile as pure alcohol.
A convenient apparatus for the preparation
of alcohol, on the small scale, is that figured in the engr., and which will be self-explanatory to every one competent to use it. The tank (i) should be supplied with ice-cold water; and the receiver (g) should be covered with cloths kept continually wet with water of the same temperature. The capsule or basin (c) is a water bath heated by the little gas furnace (d). On the large scale, for commercial alcohol, a copper still, fitted with a glass refrigeratory and receiver, is commonly employed.