Besides Calvert's soaps, containing epecific proportions of carbolic acid, there are two prepa rations of the acid which call for a short notice, viz. carbolized powder and carbolized tow. The former consiets of a mixture, in the proportion of 15-20 per cent., of liquid carbolic and eresylic acids, and an inert base, such as silica. Perhaps silicate of alumina, or china clay, is the best; Hate, which is sometimes used, is not so suitable, on account of its destructive nature to carpets, &c., should it by accident be spilled ou them; it would also set free ammonia, if present in the matter to be disinfected. In this manner, is produced a disinfecting powder, in which the acid ia left in a free state, thus allowing it to act by direct means, or by evaporation.
— In order to readily detect the amount of real carbolic acid in a disinfecting powder, R. Le Neve Foster, F.C.S., has devised the following rough method :—Place 1000 gr. of the powder in a small tubulated retort ; heat the retort gradually, until the liquid distillate ceases to drop (a brisk heat is required towards the end of the operation); collect the diatillate, which will condense in the tube of the retort, in a graduated cylinder grain measure, and allow it to settle for one hour, when the amount of oily liquid and water may be read off ; the oily liquid should represent the amount of carbolic acid ; to ascertain if thia be ao, to one volume of it, add two volumes of a solution of pure caustic soda, 14° Tw. at 15° (60° F.), which will entirely dissolve the carbolic acid.; if any remains undissolved, it will probably consist of either heavy or light oil of tar, the moat frequent adulteranta of carholic acid, and, in some eases, entirely substituted for it. The above process will, if carefnlly worked, give within per cent. of the amount of carbolic acid really contained in the powder.
Carbolized tow is a preparation of tow with carbolic acid ; it is recommended by the British Medical Journal,' in decided and unqualified terms, and may with advantage be used for most of the surgical purposes to which lint, sponge, and cotton wool are now applied.
Other proposes to produce colourless cryatallized carbolic acid, in the following manner. Raw phenate of soda is thoroughly heated in a copper still ; water, naphthalene oils, and a little carbolio acid pass over, and the fire is removed when the distillate begins to run milky : 15 kilos. require about ten hours. The greater part of the carbolic acid remains combined with the soda, as a solid mass ; the temperature of the vapour during distillation may reach 170° (338° F.); the solid residue is afterwards dissolved out in triple the quantity of water necessmy. This liquid is allowed to settle for some days, when certain impurities are deposited. Dilute sulphuric acid is then added to the clear liquid, the carbolic acid is decanted and distilled in glass vessels ; water passes over first, then pure carbolic acid, which crystallizes entire, and lastly a less pure carbolic aoid, which, even after crystallization, retains some oily impurities. In order to
obtain carbolic aoid in'a dry state, recourse must be had to digestion with chloride of calcium, followed hy a new rectification ; if required pure, only that portion which boils at 188° (370° F.) muat be received ; the distillate, hy refrigeration, furnishes crystals of the acid, which must be drained, dried, and preserved from contact with the air.
To ascertain the percentage of carbolio acid in dead oils, &a., there is a simple method, based upon the boiling point of the acid. The substance is heated in a still, and the oily liquid distilling at 150°-200° (302°-392° F.) is well mixed with solution of caustio soda, which combines with the carbolic acid, forming a compound which may be readily decomposed by any strong mineral acid. Briefly, the process amounts to a preparation of carbolic acid, carried on so carefully as to render it auitable for ascertaining quantities.
Professor Church remarks that the rank of carbolic acid as a most valuable contribution from chemistry to medicine is so well aasured as to require no confirmation, yet there ia an objection urged against the substance, which has some apparent force, simply beoause the preparations of commerce are ao seldom free from a gas-like or naphthaiic odour, which, though entirely foreign to carbolic acid itself, has condemned its use in some quarters. He adopted the following simple plan of purifying such acid :-1 lb. of carbolic acid is poured into 20 lb. of cold distilled water, taking care not to permit the whole of the acid to enter into solution. With a good sample, if after repeated shaking at intervals, 2-3 ounces of the acid remain at the bottom of the vessel, this will be sufficient to hold all the impurities ; with bad samples, less water or more acid must he used. The aqueous solution is siphoned off, and filtered till perfectly clear ; it ia then placed in a oylinder, and common salt is added'with agitation till it no longer dissolves. On standing, the groater part of the carbolic acid will be found, as a yellow oily layer, on the t,op of the saline liquor, and may be removed for use. As it contains 5 per cent. or more of water, it does not generally crystallize ; but it may be made to do so by distilling it from a little lime. The portion collected up to 185° (365° F.) or thereabouts has, at ordinary temperatures, scarcely any odour, save a faint one resembling that of geranium leaves. The saline liquor remaining may be distilled, to yield a seoond portion of pure carbolic acid, which will serve as a disinfectant and deodoriser.