Quantities so small as 1 part per 1000 control the fermentation of liquors, and prevent the formation of moulds on the surface, economising tannin, and preserving vegetable acids already present, but at the same time lessening their production by fermentation, and therefore sometimes leading to difficulties in the early stages of tanning. Carbolic acid is not, strictly speaking, an acid, but rather of the nature of an alcohol, although it forms weak combinations with bases. It is a powerful narcotic poison, and if dropped on the skin in a concentrated form it produces severe burns; these are best treated with oil, while in cases of poisoning, oil and chalk must be administered internally, but if the quantity of carbolic acid taken has been large, are not likely to be effective. From its cheapness and efficiency, carbolic acid is likely to be increasingly used, although for special uses some of the newer antiseptics have great advantages.
Eudermin is a tar-oil manufactured by Speyer and Grund, of Frankfort-on-Main, which is intended as an antiseptic addition to stuffing greases to prevent mould and spueing. It is recommended for the purpose by Eitner[10] and can be used in proportions such as 10 per cent. of the grease. Creasotes and cresols can be dissolved in oils and stuffing greases, and act as antiseptics, though less powerfully than in aqueous solution. Rosin oils and turpentine have also antiseptic properties.
[10] Gerber, 1893, p. 41.
Creasote, “heavy coal oil,” or “dead oil,” is a complex mixture of hydrocarbons, phenols and cresols, obtained by distillation of coal tar, heavier than water, and almost insoluble in it. It is largely used as a preservative for timber. Carbolineum is an oil of this class, boiling at over 300° C., and intended for application to wood. One or more coats are applied to the dry wood at a temperature of 80° C. The workman’s hands must be protected by gloves, as the hot creasote raises painful blisters. Eitner[11] recommends its use for preserving pits, posts and other woodwork in tanneries. Wood-creasote is a somewhat similar product obtained from wood-tar.
[11] Gerber, 1889, p. 183.
The heavier cresols are so little soluble in water as to be valueless in their ordinary form as antiseptics, but several preparations are made under the names of “Creolin,” “Jeye’s fluid,” “Lysol,” “Izal,” “Soluble phenyl,” etc., in which they are treated with additions of soap or alkalies, which cause them to emulsify or dissolve in water, generally as milky liquids. These are powerful germicides and have the advantage over phenol of being non-poisonous. 0·1 to 0·5 per cent. solution of creolin will sterilise hides after bating so that no putrefaction takes place in the liquors. Mr. J. T. Wood specially recommends creolin for the general purposes of the tannery, disinfecting pits and tubs, and for checking the action of puers and drenches on goods which have gone a little too far, by throwing them into a 0·2 per cent. solution.
Salicylic acid, orthohydroxybenzoic acid, C6H4OH(COOH), is now artificially prepared from phenol. It is much less poisonous than the latter and has no smell, which makes it valuable for certain purposes, but is too dear for most technical applications. Many bacteria appear to become gradually habituated to its action, and the same is true of phenol to a less degree.
Salicylic acid is closely related to protocatechuic and gallic acids, and, like these, gives a blackish colour with iron salts. It is freely soluble in hot water, but very sparingly in cold. The addition of 1-21⁄2 parts of sodium phosphate, sulphate, or potassium nitrate to each part of salicylic acid greatly increases its solubility. It seems much more powerful in preventing the development of bacteria than carbolic acid; a solution of 1 part of salicylic acid in 666 of water is said to be equal in this respect to 1 part of carbolic in 200.
Benzoic acid, C6H5COOH, though not much employed, except in medicine, is a still more powerful disinfectant, and has the advantage of being non-poisonous to human beings.
“Cresotinic acid,” which is derived from the cresols as salicylic acid is derived from phenol, is more soluble than salicylic acid. It is not very poisonous, and a powerful disinfectant. In a crude form it has been introduced by Hauff, of Feuerbach, for bating or removing lime from hides. This it does very well, though without the softening action of a true bate. It has a tendency to produce a pinkish stain, and in some degree a sort of tanning of the fibre. Its price, moreover, is rather high for extensive technical use. (See also [p. 162].)