As an antizymotic, this is among the most efficient substances in our possession, scarcely less so than sulphurous acid, while less disagreeable and offensive than that in its gaseous form. There appears, however, to be a close resemblance, in this respect, between it and two other products of similar origin, cresylic acid and creasote, and it is uncertain how far, as commonly sold in the shops, they are distinct from one another. Creasote, as originally discovered by Reichenbach, was obtained from wood-tar, or the products of the distillation of wood; carbolic and cresylic acids are derived from coal-tar; but what is now sold as creasote in the market is thought, for the most part, to have the latter origin, and to consist mainly either of one or both of these acids, or of the acids mixed with the product of wood-tar. But creasote having been already treated of (vol. II. p. 632), we are now to consider carbolic acid in its pure or unmixed state. Unfortunately it has received various names from chemists, as phenic acid, phenylic acid, and phenol; and the reader, when he meets with these titles, must recollect that they are mere synonymes of the one placed at the head of this article.

Pure carbolic acid is at ordinary temperatures a solid body, white and crystalline, melting at 95° F., and distilling at 370°. On exposure to the air it rapidly deliquesces, and is soon converted into an oily liquid. The addition of water or of cresylic acid also renders it liquid, and in the shops it is almost always kept in that form. its sp. gr. is 1.062. it has an odour analogous to that of creasote, yet distinct, and a hot acrid taste. it is soluble in 20 parts of water, and freely in alcohol; and its solubility in the former liquid is greatly increased by the addition of the latter, or of acetic acid. Though neutral to test-paper, it combines with salifiable bases, and has, therefore, been ranked with the acids; but its power of combination is very feeble, as even carbonic acid decomposes its salts. it is distinguished from creasote by its greater density, its solid form when pure at common temperatures, its lower boiling point, and by yielding different products under the action of nitric acid. For the mode of its preparation the reader is referred to the U. S. Dispensatory. Cresylic acid, which is also obtained from coal-tar, and with which it is said to be often mixed as existing in commerce, is liquid at ordinary temperatures; and its boiling point is considerably higher than that of carbolic acid, being about 400° F. The latter is among the products when coal-tar is distilled at a heat between 300° and 400°, the former at 400° or upwards. No injury results from their mixture; as cresylic acid has been proved to possess at least equal antiseptic powers with carbolic acid. An important chemical property of this substance, which it shares with creasote, is that of coagulating albumen.

Effects on the System, and Medical Uses. Applied undiluted to the skin, carbolic acid acts as a powerful irritant, causing a sharp pain, lasting about an hour, with a white appearance ascribed to the coagulation of albumen, and followed by severe inflammation with exfoliation of the cuticle. it operates in like manner on the mucous membranes; and, if applied for a sufficient length of time, will even act superficially as an escha. rotic. Taken internally, it appears to operate similarly to creasote, and has been used for similar purposes. it has been given advantageously in vomiting and diarrhoea, and in the gastric pains of dyspepsia after eating; and is said to have cured spasmodic asthma. But it has been much more employed as a local remedy, and often very successfully. injected into the rectum, it injures or destroys the threadworm, and favours its expulsion by purgatives or enemata. it is also extremely destructive to the insect of scabies. As a superficial escharotic, it is adapted to the diphtheric patches, sloughing ulcers of the fauces, and to cancerous and gangrenous surfaces generally, in which its power of correcting fetid odours comes usefully into play. it ought to prove highly serviceable in hospital gangrene. Sufficiently diluted, it may be used in fistulas and hemorrhoidal disease; and is an excellent application in various cutaneous affections, as lepra and psoriasis, porrigo or favus, and the advanced stages of eczema and impetigo. in all these cases, it may be employed dissolved in water or in glycerin, which takes it up in all proportions. The watery solution may be made by adding 40 parts of hot water to one of the carbolic acid, shaking thoroughly and filtering. This may be employed as a wash to correct fetid odour in all gangrenous, ulcerative, or suppurative affections. in necrosis of the bones with ulceration, it may be injected through the fistulous openings. An emulsion may be made by mixing one part of the acid with eight parts of water, sweetened with one or two parts of sugar. An ointment for external use may be prepared by rubbing one part of the acid with fourteen parts of spermaceti. M. Bazin recommends very highly a solution of one part of carbolic acid in 40 parts of acetic acid of 8° B., and 100 of water, as a local remedy in tetter and the itch. A single application, he says, will destroy the insect of the latter disease. The power of coagulating albumen renders the acid useful for controlling hemorrhage from bleeding surfaces. For internal use a drop may be given in half a fluidounce or a fluidounce of sweetened water.

Powers and Uses as a Disinfectant and Antizymotic. it has been known, since the publications of Prof. F. Crace Calvert, of Manchester, that carbolic acid, besides coagulating albumen, had the power not only of deodorizing fetid animal substances, but of arresting fermentation, destroying the lower forms of animal and vegetable life, preventing mouldiness in vegetable juices, and protecting animal substances against putrefaction. The knowledge of these properties very naturally suggested its use as one of the means for arresting the cattle plague, recently so prevalent and destructive in England; and Dr. Angus Smith and Mr. Win. Crookes, who were officially engaged in investigating the subject, had their attention especially directed to this agent, as promising favourable results. in various forms, considered as the representative of all similar bodies, it had been employed as an antiseptic from very early times. As the ingredient to which tar and pitch owe what disinfectant and preservative powers they possess, it was probably used by the ancient Egyptians in embalming their dead; and the long-known efficacy of smoke in preserving meats depended on the same cause. in fact, tar and pitch were popular remedies in the cattle plague during a former prevalence in England, in the preceding century. it was, therefore, one of the most obvious subjects for investigation on this occasion. The first point was to ascertain to what, precisely, was its known efficacy in obviating the effects of putrefaction ascribable. Could it be owing to a chemical agency, like that of the oxidizing or deoxidizing disinfectants ? it was soon determined by experiment that it had no power whatever in causing or promoting oxidation. From the same experiments, in which it was shown that not the least effect was produced on the oxidation of bodies, which went on in the presence, exactly as in the absence of carbolic acid, it was equally inferrible that it owed none of its influence to a deoxidizing power. Could this influence be ascribed to its property of combining with and coagulating albumen ? The contrary of this was shown, conclusively, by the small extent to which this power was possessed. An interesting experiment seemed to render it probable that the effect produced by it is altogether independent of chemical agency. A piece of putrefying meat was divided into two parts; one was steeped for half an hour in solution of chlorinated lime, then washed, and hung up to dry. The offensive smell could not be perceived at the time of suspension. it had entirely disappeared. The other piece was soaked in a solution of carbolic acid containing one per cent. of the acid; and it, too, was hung up to dry, still, however, retaining the putrid smell, though somewhat covered by the smell of the carbolic acid itself. in the course of two days it completely lost its offensive odour. After a few weeks, both pieces were again examined. The piece which had been immediately sweetened by the chloride of lime, was now as offensive as at first; that to which the carbolic acid had been applied, was simply dried, and had no offensive odour whatever; and a month afterward, it still continued perfectly sweet. By various other experiments it was shown, beyond doubt, that all forms of animal matter could be indefinitely preserved from putrefaction by the carbolic acid, even in very small quantities. Now the inference from all this is that, though this agent may have some power of correcting offensive odour by combining with and neutralizing the odorous effluvia, yet that its extraordinary preservative and antiseptic powers must be ascribed to some other agency. it undoubtedly has the power of suspending the action of putrefaction itself. Other experiments proved that it has the power of promptly arresting the common vinous fermentation. The question now to be solved was, whether it checked the ordinary putrefactive fermentations by catalytic influence, that merely of its presence, or whether its action might not be explained in a more satisfactory way. For this purpose, a great number of minute animals, as cheese-mites, fleas, gnats, numerous species of infusoria, etc., were submitted to its influence; and all instantly perished. Now the presence of living beings, in great multitudes, in all known instances of fermentation, is an admitted fact. What conclusion can be better warranted than that the carbolic acid operates in preventing and arresting fermentations, and of course in preventing all the offensive and noxious effluvia from such sources, by destroying the life of the organized beings which support them ? it was, therefore, fairly concluded that this agent might be employed, with some hope of success, in preventing the spread of the cattle plague, probably dependent on the action of these microscopic agents, giving rise, by their entrance, or that of their spores or ova, into the system of the animals, to the disease of which so many perished. Another experiment is worth mentioning. The air from a close shed, in which were several animals dying of the disease, was drawn forcibly through a glass tube containing raw cotton. One portion of the cotton was exposed to the vapour of carbolic acid, another, not. Two calves, apparently healthy, were selected, and both were inoculated by incision; one, with the cotton which had not been acted on, the other, with the portion infected. The former remained perfectly well, the latter was attacked with the disease, and died in a few days. Sufficient encouragement was thus afforded for the practical application of the preventive. Accordingly, a solution of carbolic acid in water, containing one per cent. or more of the acid, was largely employed, in connection with sulphurous acid gas, in all possible methods, in the hope that it might destroy the cause, and prevent the extension of the disease; and, according to the official report of Mr. Crookes, with the most satisfactory results. There was reason to think that its internal use, given by the stomach and injected into the veins, was beneficial in its influence on the disease, ameliorating the symptoms, postponing the fatal issue, and sometimes apparently contributing to a restoration to health. The inference from all this is irresistible in favour of using carbolic acid, as a preventive, in all complaints having their origin in contagious or infectious effluvia. The solution, containing one or two per cent. of the acid, should be used by washing with it solid bodies to which the morbid cause might be supposed to adhere, by adding it to all infected liquids, by hanging up cloths wet with it in the infected air, and by diffusing it through the air in the form of spray, by means of an instrument such as the atomizer. It may even be tried internally, in the same set of diseases, when not decidedly contraindicated by the symptoms, in the hope that it may modify the influence of the poison in the blood, by suspending any possible existing fermentative process.