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water, cent, spirit, spirits, deg, quantity, pure and gr

ALCOHOL (Formula, ; molecular weight, 46 ; synonyms, ethylic alcohol, aqua vita', spirits of is obtained by carefully distilling any spirituous or fermented liquor. If wine or beer be placed in a suitable retort and heat applied, the alcohol may be separated from the less volatile matter, and thus obtained it is known in commerce as "rectified spirits of wine." Its specific gravity is usually about 0.840 to 0.850, and it generally contains about 17 to 20 per cent. of water, because although the alcohol is far more volatile than the water, and rises first and is condensed in the receiver, yet a portion of the water also passes over with the alcohol in the proportion already mentioned, and dilutes it to that extent. This water may be removed by adding to it carbonate of potash until that salt ceases to dissolve. This mixture is then thoroughly shaken, and when allowed to stand at rest soon separates into two portions—the uppermost part is the alcohol and the lowermost an aqueous solution of the carbonate. The alcohol portion is then carefully drawn off by means of a syphon and poured upon a quantity of powdered quicklime of the same weight as the alcohol, and previously placed into a tabulated retort. This is allowed a day or two to digest, and then slowly distilled in a water bath at a temperature of about 200 deg.

Alcohol is a limpid, colorless liquid, of an agreeable odor and a strong, pungent taste. From its action on the system it may be termed poisonous, and if diluted it is very intoxicating. It absorbs vapor of water, and becomes diluted by exposure to damp air ; it requires, therefore, to be kept in a well-stoppered bottle. It has never been frozen. It is extremely inflammable, and burns with a pale bluish and smokeless flame, scarcely visible in daylight, but the heat of the flame is very intense.

The best test for alcohol is to mix with a little solid iodine and then to add a weak solution of caustic potash until the liquid is nearly decolorized. On stirring a yellow crystalline precipitate of iodoform will be formed.

The uses of alcohol in the photographic art are very numerous. Besides many other purposes to which it is put its power of dissolving pyroxyline (gun-cotton) and various gum lacs and resins causes it to be largely used in the manufacture of collodion and different varnishes. It acts as a preservative of pyro, owing to the fact that atmospheric oxygen does not dissolve in it as rapidly as in water. It is used for drying negatives quickly on account of its strong affinity for water. It has also a hardening effect on gelatine and is used in the prevention of frilling.

Alcohol is also added to dry plate emulsions. It causes them to flow more evenly over the glass plates and accelerates the drying process. About 5 per cent. is the usual quantity. If too much be added, it will cause spots. Alcohol in a gelatine emulsion also acts as a preservative while the emulsion is in the jelly state.

It is not really essential that absolute (pure) alcohol should be used for all photographic purposes, as it is very expensive to manufacture. A spirit that contains less than 4 per cent. of water is quite pure enough, and may be obtained by agitating commercial spirits of wine with carbonate of potash, and then with quicklime in the manner already advised.

The principal impurity in commercial alcohol is fusel oil. This may be detected by first distilling nine-tenths of the alcohol at lowest possible temperature ; the residue is then allowed to cool thoroughly and shaken up with an equal volume of pure petroleum ether. The upper layer of ether is syphoned off into an evaporating dish and evaporated to dryness at 8o deg. C., when fusel oil will be at once detected in the residue by its unpleasant and characteristic smell * Rectified Spirit (Formula, contains 16 per cent. of water and 84 per cent. of alcohol. Sp. gr. about .838.

In rectifying spirits, it is sometimes, for economy's sake, adulterated with a liquid known as "faints," and as these faints are usually contaminated with essential oils, it is necessary that such should be avoided. Grain spirit is to be preferred, the specific gravity of 'which varies from .817 to .819 at 6o deg. Fahr. Its smell is very sweet, and although it may not be strong enough for many purposes, a portion of it can be converted into alcohol of .805 by means of dry chloride of calcium, and this mixed with the remainder. The re-action to test paper of this spirit should be quite neutral ; but if, as sometimes happens, a trace of acid is present, one drop of a solution of ammonia, sp. gr. 0.93, will neutralize it.

The following table shows the quantity of absolute alcohol (sp. gr. .796 at 6o deg.) contained in diluted alcohol of different specific gravities : To get the exact measurement, other impurities must not be present, but must first be removed by distilling seven-eighths of a measured volume of the spirit and adding sufficient water to make up the original volume.