ANILINE GREYS.—Abers grey is thus obtained :-2 lb. aniline, boiling at 188° (370° F.), ia mixed with 10 lb. solution arsenic acid (sp. gr. 1.375), and heated in a water bath till the mixture thickens and risea. The vesacl ia then withdrawn from the fire, a,nd a little water is poured in, to prevent boiling over. The product is thick and blaakiah, and is insoluble in water. It is purified by adding 18 qts. water and 2 lb. hydrochloric acid, boiling for about half an hour, and filtering ; the precipitate is washed with boiling water, and finally with a weak aolution of sodic carbonate, so as to neutralize the acid, after which it is dried, and remains as a fine black powder. Its aoltition is effected in alcohol, to which 10 per cent. sulphuric acid may be added, and will produce inany ahades of grey by addition of the requisite mordants to the bath.
Greys are obtained from weak solutions of some blacka. One is prepared by Caathelaz by mixing 10 parts by weight of Perkin'a violet with 11 parts oil of vitriol, and 6 parts aldehyde, and heating for four to five hours. The colour is precipitated, from its dilute solution, by an alkali, and washed.
A recent application of the aniline dyes is for the production of coloured laequera ; the salts used should be as free as possible from water. They are also employed to sepazate cotton from woollen rags, the former taking no colour from a dye which produces a pronounced tint in the latter. ' Carbolic also p. 41.) This compound is now regarded as benzol, one atom of whose hydrogen haa been replaced by the radical HO ; its formula is therefore C,H,(I10), benzol being C6LIG. When in a pure atate, it consists of colourless acieular crystals, and has a sp. gr. of 1.065 ; Calvert's " Pure Medicinal" acid fuses at 42° (108° F.) to an oily liquid, and boila 182° (359° F.). Carbolic acid is one of the most powerful antiseptic and antizymotic agenta at present known, and exhibits strong anresthetic and escharotic properties. In the animal king-dem, it is found in the urine of men, horses', and cows ; in the vegetable world, it exists in the eaator plant, in the Andromeda Leschenaultii, a plant growing on the high lands of India, and in the resin of the Zanthorrhcea hastilis ; among minerals, coal seems to be the only one in which it has hitherto been discovered. It may be produced by the action of nitrous acid on aniline, and by the dry distillation of gum ben,zoin, quinic acid, and chromate of pelosina ; there is besides the ordinary commercial process of extracting it from the oils of coal-tar.
Early Methods of Manufacture.—So long ago as 1831, carbolic acid was discovered by Runge to be a constituent of coal-tar oil ; and about seven years later, Laurent rnade further investigations into its properties, and succeeded in separating it. He considered it to be a hydrated oxide of a peculiar compound radical, phenyl, whence he named it hydrated oxide of phenyl. Mansfield, in 1847, and Boboauf, in 1856, rnade some improvements in the processes of extraction ; but it was reserved for the late Dr. Crace Calvert and bis partners to work out the manufacture, to such perfection as would enable the acid to be produced at a saleable figure on a large scale ; and his firm is now the largest, as it is undoubtedly the first, in this branch of chemical industry.
Laurent's method of preparing carbolic acid frorn coal-tar consisted in submitting the light oils to a fractional distillation, and then treating those products which had distilled over at tempera tures varying from 160° to 218° (320° to 421° F.) vvith a concentrated solution of potash, separating the alkaline solution from the hydrocarbons which floated on it, and afterwards neutaalizing the alkali by an acid, which last process liberated the carbolic acid from the alkaline solution. Pure carbolic acid was present, however, only in very srnall proportion. The product was, in fact, a mixture cornposed chiefly of different liquids, similar in properties and composition to carbolic acid ; and, though Laurent succeeded in obtaining solid carbolic acid, the process devised by him was too expensive to answer on a manufacturing scale, and his mode of operation was too complicated. The modifications suggested by Mansfield, and later by Boheeuf, consisted principally in employing caustic soda instead of potash, and in treating the whole of the light oils, instead of only a special portion of them ; still the result was a highly impure acid, from which it was very difficult to extract the pure acid. Commercially, however, their process was a step in the right direction, and was employed by Clift, under Dr. Calvert, in manufacturing sorne carbolic acid, about thirty years ago. This impure acid was successfully used, by Dr. Calvert, in producing picric acid, in preventing the transformation of tannic acid into gallic acid, in tanning, and in the preservation of subjects for the dissecting-room.