Popular Science Monthly/Volume 7/October 1875/A New Antiseptic
CHEMISTS have long been familiar with the substance known as salicylic acid, and in the text-books most of its properties are described, as also the various modes of preparing it. Its most valuable property, however, namely, its action as an anti-ferment and anti-septic, was discovered only about a year ago, by Prof. Kolbe, of the University of Leipsic. Salicylic acid exists ready-formed in the flowers of Spiræa ulmaria (meadow-sweet), and as methyl-salicylic acid in oil of wintergreen. It is also prepared from indigo and from salicin, a substance found in the bark of several species of willow and poplar. But the best mode of preparing it is that proposed by Kolbe and Lautemann, which is thus described by Watts:
Dry carbonic anhydride is passed into warm phenol, with addition of small pieces of sodium. The metal then dissolves, with evolution of hydrogen, and a stiff paste is formed, containing the isomeric salts, salicylate and phenyl-carbonate of sodium, together with unaltered phenol. On acidulating with hydrochloric acid, the phenyl-carbonic acid is decomposed, with evolution of carbonic anhydride, and the salicylic acid which is set free may be separated from the phenol by solution in strong aqueous carbonate of ammonium. The solution, boiled down till it acquires a slight acid reaction, filtered from separated resin, and mixed with hydrochloric acid, yields salicylic acid, to be purified by recrystallization with the aid of animal charcoal.
Reasoning from the fact that salicylic acid can thus be prepared from phenol and carbonic acid, and from the further fact that on the application of heat it again splits up into those two acids, Kolbe was led to inquire whether it possessed the antiseptic properties of phenol. The value of the latter substance as an anti-ferment is well known, but its poisonous properties, as well as its disagreeable smell and acrid taste, render it unsuitable as a means of preserving articles of food, or as a medicinal agent. It was evident, therefore, that if salicylic acid, which is odorless, almost tasteless, and, when taken in small quantities, innocuous, possessed antiseptic properties equal to those of phenol, one of the most urgent wants of modern life would be at once supplied. Experiment proved the conjecture to be correct, and thus many years of theoretical investigation were crowned by practical results of the highest value.
Among the experiments made with this substance we may mention the following: Brewer's yeast (quantity not stated), which causes alcoholic fermentation of sugar, was found to have no effect upon a solution of glucose containing the one-thousandth part of salicylic acid. Half a gramme of the acid suffices to check the fermentation produced by five grammes of beer-yeast, acting on 120 grammes of sugar dissolved in a litre of water. Experiments made by Neubauer show that 100 grammes of salicylic acid suffices to absolutely prevent fermentation in 1,000 litres of must, or fresh-pressed juice of grapes. Flour of mustard, which, when mixed with lukewarm water, gives out the pungent oil of mustard, is perfectly odorless when a small quantity of salicylic acid is added to it. So, too, this acid prevents the action of emulsin (the ferment contained in almonds) upon amygdalin, and the conversion of the latter into oil of bitter-almonds. Milk treated with 0.04 per cent, of salicylic acid remained uncoagulated for thirty-six hours longer than milk not so treated. In like manner a litre of beer, containing one gramme of the acid, and exposed to the air, did not become sour after standing for a considerable time, nor was there the slightest trace of mould. As a means of keeping water sweet on shipboard it is specially valuable.
Eggs immersed for an hour in a solution of salicylic acid were at the end of three months as fresh as at first. Flesh-meat dusted over with the acid keeps its freshness for weeks. When about to be used, the meat may be dipped into water, to remove the acid.
Dr. Thiersch, of the Leipsic Hospital, has used this substance "with very favorable results" in his surgical practice. Kolbe has employed it as a wash for the teeth and mouth, and asserts that it is very effectual in purifying the breath. In a communication published in the Journal für praktische Chemie, he says: "As a medicine for internal use, salicylic acid does not seem to have been much employed hitherto, and yet, owing to its antiseptic properties, it is indicated in all diseases of the blood, especially in those which are developed by contagion." Among the diseases likely to yield to this treatment he names scarlatina, diphtheria, measles, small-pox, syphilis, dysentery, typhus, and cholera. Further, he is inclined to think that it might be effectual in dealing with pyæmia and hydrophobia.
Dr. Karl Fontheim, writing to the same journal, says: "This new remedy has been found of very special benefit in treating diphtheria; I have employed it in thirty-two cases; of these none have proved fatal, and the worst cases recovered in eight days." Prof. Zürn, of Leipsic, has employed salicylic acid in veterinary practice, both medical and surgical, and it is his opinion that "for internal and external use in domestic animals, as an antiseptic and destroyer of living contagia, it is destined to occupy as honorable a position in veterinary practice as it does in human medicine."
Kolbe has experimented on his own person, to determine whether or not salicylic acid is injurious to the animal economy. For several days in succession he took daily, in four parts, one half-gramme (solution in water 1: 1,000), without the slightest bad effect. After an interval of eight days, he for five successive days took double the former dose, and for two successive days he took one and a half gramme. In the mean time his digestion was entirely normal; there was no feeling of oppression in the stomach, nor did he experience any inconvenience whatever. Other physicians who, at his request, made the same experiments, confirm these results. Still the remedy must not be taken in the form of a powder, for in that shape it attacks the mucous membrane of the mouth and œsophagus; it must be taken in solution.
F. von Heyden, of Dresden, manufactures salicylic acid on a large scale, according to the process of Kolbe and Lautemann. The product is a yellowish-white powder. This is the crude acid, which may be employed for disinfecting purposes. When intended for preserving articles of food, or for medical or surgical uses, this crude acid must be purified, and then its color is snowy white. Rautert has succeeded in sublimating it completely in a current of superheated steam, thus readily obtaining it pure. Recrystallization from hot distilled water gives it in the form of slender needles an inch long.