There are several substances much used as disinfectants, which probably act, so far as they are mere chemical agents, by combining with and neutralizing the products of organic change; though this can scarcely be said to have been demonstrated of any one of them. These belong to two wholly distinct categories, one of which includes mineral substances only, the other only substances of vegetable origin. The former are believed to have no other than a chemical action, and to be capable only of neutralizing the noxious effluvia as fast as they are generated, so that if entirely removed their effect would cease; the latter not only do this, but destroy the vital source of the fermentative processes, and therefore have a permanent influence. The chlorides of zinc, iron, manganese, and sodium belong to the first division, and are said to be efficient in the order in which they are here mentioned; carbolic and cresylic acids, creasote, and coal and wood tar belong to the second.

Carbolic Acid, with the analogous substances, will be specially noticed with the antizymotics. it will be sufficient here to say that they are among the most efficient disinfectants, being particularly qualified for this purpose by their volatility; and that they also possess extraordinary powers in rendering inert or destroying the causes not only of offensive effluvia, but also of those peculiar poisons which cause contagious and other specific fevers.

Chloride of Zinc is the only one of the chlorides, except the chloride of sodium so largely used in the preservation of organic material for domestic use, much employed as a disinfectant. it has been already described among the escharotics (vol. II. p. 805), where all its characteristic properties are sufficiently noticed. There is said to be little difference in efficiency between this and sulphate of zinc; and, as the latter is the least costly of the two, it will probably in time supersede the former. Both, being non-volatile, are somewhat restricted in the limits of their application. The solution of the chloride has been used for several years under the name of Burnett's disinfecting liquid, and is sometimes also called Drew's disinfectant. it is employed for deodorizing the discharges in the sick chamber, and might be applied for the same purpose on a large scale, as in the disinfecting of privies, sewers, etc.; but its cost is here a great objection. According to Dr. Letheby, Health Officer of the City of London, the solution should contain from 50 to 54 per cent. of the solid chloride, and should have the sp. gr. 1.594. A tablespoonful is sufficient for each discharge from the bowels.

Chloride op iron operates precisely as the chloride of zinc, and may be used for the same purposes, and in the same way. The solution for use should have the sp. gr. 1.470, and should contain 40 per cent.of the chloride. (See vol. i. p. 461.)