Carbolic Acid Disinfecting Powders differ considerably in their nature according to the material used as a basis and the proportion of carbolic acid introduced. In some cases, the basis of the powder is slaked lime, but the resultant "carbolate of limo" has been proved to be of little value for disinfecting purposes. " Maedougall's Disinfecting Powder" is made by adding a certain pro portion of crude carbolic acid to an impure sulphite of calcium, prepared by passing sulphurous acid over ignited limestone. The produet often contains far more sulphate than sulphite, and not unfreqnently contains free lime, which reduces its disinfecting value. " Calvert's Carbolic Acid Powder" is made by adding carbolic acid to the silicious residue resulting from the manufacture of sulphate of aluminium from shale. Sand, clay, and other materials are sometimes used. Good carbolic acid powders should contain at least 12 or 15 per cent of crude carbolic acid. They are liable to lose 1 or 2 per cent. of the acid by volatilization. Some powders in the market contain only 4 or 5 per cent. of total oils, of which less than half are really carbolic and eresylie acids, the remainder being worthless tar-oil.
The proportion of crude carbolic acid contained in silicious carbolic acid powders may be readily ascertained by the following proeess. 1000 grains of the sample are placed in a retort and heated
over a flame. Crude carbolic aoid distils over and may be collected in a graduated tube. The process is continued till nothing more distils. The heat should be pushed to dull redness and the retort occasionally shaken. On standing, the aqueous portion of the distillate separates from the oily liquid, and the volume of the latter may be read off. The lose in the process is usually about •8 per cent., which may be added to the result obtained. The crude carbolic acid obtained may be examined for neutral coal-oils by the process described above.
The manufacture of carbolic acid is of comparatively recent growth, having been originated by the late Dr. F. Crace Calvert, of Manchester. The manufacture is probably increasing, but is still chiefly confined to Manchester and the neighbourhood, and is in comparatively few haude. The manufactured article is disposed of chiefly to wholesale chemists, druggists, and drysalters; to the manufacturers of dyeing materials and disinfecting powders, and in other ways indieated by the uses to which the article is put. (See also article on " Coal-tar Products.") A. H. A