ANTISEPTICS are substances which arrest the putrefactive changes that dead vege table and animal matter is liable to undergo when exposed to air, warmth, and moisture. A. are therefore anti-putrescents; and the term itself indicates the office which the members of the class fulfill (anti, against, and septikos, putrefactive). The theory of the action of all A. is, that one or two of the three indispensable conditions of putre faction—viz., 1, a moderate warmth, 2, access to air, and 3, moisture—are arrested or neutralized. Thus, in the preservation of fish in stores or during transport by railway, they are packed in barrels with ice, which keeps down the temperature; and though air and moisture gain admittance, yet the putrefactive processes cannot proceed. The same preservative power of cold is observed naturally in the .discovery of remains of elephants and other animals imbedded in the ice of the polar regions, and which doubtless have been locked up there for ages. In a less degree, the influence of cold as an antiseptic is observed in the longer time that meat, eggs, and other animal matters keep fresh in winter than in summer.
Again, warmth and moisture may be present, but if the air be excluded, putrefac tion does not go on. The ordinary mode of preparing preserved meats affords the best illustration of this point. The substance to be preserved is placed in a tin dish cov ered over, and leaving a very small opening. When the can with its contents is heated, the air which fills up the pores of the solids, and is dissolved in the liquids, is driven off, and escaping by the aperture in the cover of the dish, leaves the con tents devoid of air. If the opening-be now closed with solder, the air is kept from returning; and whatever climate the can of preserved meat be sent to, yet so long as the tin casing remains good, and refuses to admit the air, so long will the contents continue wholesome and palatable. The common plan of preserving eggs by rubbing over the shell with tallow or oil, is founded on the principle of filling up the pores of the shell, so as to deny the admission of the air. Moisture is likewise necessary for the process of putrefaction. Thus, if the contents of an egg be thrown out on a plate, and thoroughly dried in an oven, the whole becomes of a hard, horny consist ence, and may be kept in this state for years without exhibiting the slightest symp tom of passing into a putrescent or rotten condition. In the same way meat may be kept quite fresh by depriving it of moisture. Eggs dried up in this manner require only to be soaked in cold water, and then boiled, when they will present themselves in a condition hardly differing in flavor and taste from an ordinary boiled egg.
The more important chemical A. are—alcohol, wood-spirit, creosote, pitch-oil, coke-oil, sugar, tannic acid, sulphurous acid, common salt, nitre, alum, chloride of zinc, sulphate of copper (blue vitriol), corrosive sublimate, arsenic.
The manner in which these A. act is very different.-1. Sulphurous acid acts by com bining with the oxygen, and thereby deoxidizing the substance. 2. Sirup of sugar acts by combining with the water of the substance to be preserved. 3. Creosote, tannic acid, alum, chloride of zinc, sulphate of copper, corrosive sublimate, and arsenic, are useful in forming compounds with the organic matter, which are not so liable to become putrescent as the uncombined organic substance. 4. Alcohol, wood-spirit, common salt and nitre, act in 'a double way, by combining with the water of the putres cible substance, and by combining with the substance itself, so as to form a more durable compound.
Some of the more important uses to which the chemical A. are applied are-1. In the preservation of anatomical specimens, where alcohol, and less often, chloride of zinc, are the agents; 2. In the curing of herring and other fish, where common. salt is generally used; 3. In preparing corned or salted meat and tongues, where common salt and nitre are jointly employed; and, 4. In the manufacture of size for writing-papers, where the paper-maker uses sulphite of soda or antichlore (containing sulphurous acid) to arrest the decomposition of the scraps of hides used in the manufacture of size. In the preser vation of timber, A. are also taken advantage of. The wood is placed in a steam-box, and the air contained in its pores being replaced by steam, the whole casing is closed tight, and allowed to cool, when the steam condenses, and leaves a vacuum in and around the block of wood. On the introduction thereafter of one of the A., it finds its way into the innermost pores of the timber. Wood thus prepared is less liable to decay thau ordinary; and the A. seem not only to withdraw water, and form durable com pounds, but to offer a poisonous dose to minute plants and animals which house them selves in the wood. The use of sulphate of copper for this purpose was suggested by Bonchardat; of corrosive sublimate, by Kyan (hence the process was called kyanizing); and of chloride of zinc, by Sir IV. Burnett (hence the term burnettizing). See also CAR BOLIC ACID, and Condy's fluid under