IRON, ACETATES OF.—Under tho name of "black" and "iron liquor," two of these salts are largely manufactured, the acetate of the protoxide and the acetate of the sesqoioxide or peroxide. Upon concentration, the former crystallizes in small greenish white needles, very soluble in water. Both solution and crystals rapidly absorb oxygon when exposed to the a'r. The is a dark red uncrystallizablo liquid, of powerful astringent taste.
Two methods 10.0 employed for the production of the ferrous acetate, or " black liquor." That usually adopted on n large scale is as fellows. Iron turnings, or indeed any refuse scrap iron, are digested with crude pyroligueous acid of El specific gravity of about 1.035, preferably at .a temperature of 66°, but occasionally in the cold. The mixture is frequently stirred to separate us far as possible the tarry matter, which floats on the surface and is skimmed off. Tho metal rapidly dissolves in the acid forming the acetate of the protexide. When ;I sample of the solution upon cooling registers a specific gravity of about Tw.), the whole is allowed to stand, the impurities are carefully skimmed off, and the liquor is ready for use. A certain quantity of hydrogen which is set tree, and the tarry products, prevent, or at least retard, oxidation into the person. Owing to this tendency to 1Lhserb oxygen, the process should be carried out as rapidly as possible—therefore with the aid of heat—and if the solution has to he kept for any considerablo length of time some metallic iron must he allowed to remain in conta•t with it.
A second method of preparation is by a double decomposition between acetate of lime and sulphate of iron. The copperas is dissolved in hot water, and added to acetate of lime liquor in the proportion of about fivo to one. Perfect decomposition is unnecessary, as a small proportion of undccomposed copperas does net injure, the liquor. This method of manufacture is more expensive than that already described, and is usually only resorted to in times of pressure. A very pure liquor is made in some of the continental works by decomposing carbonate of iron by acetate of lead, acetate of iron remaining in solution.
The persalt is obtained by decomposing a solution of sulphate of iroa—the ferric sulphate— by a solution of acetate of lime. The mixture is well agitated, sulphate of limo precipitates,
and the ferric acetate remains in solution. It has a peculiar deep red colour, and usually stands, about 25 Tw.
The acetates of iron are largely used by calico-priuters sad dyers as mordants; the protosalt chiefly by the latter, the persalt by the former. A very common mordant, " pyrolignite," (liqam,• de ferraile, bouillon noir), for black dyes, consists of a mixture of the salts, the ferrous acetate being first prepared and partial oxidation allowed. The ferrous salt produces blacks and all shades of purples and lilacs, also chocolate with acetate of alumina (red liquor). It is one of .tho most powerful of mordants, readily yielding up its acetic acid, and possessing great affinity for both fibre and colouring matter. The persalts are not such powerful mordants, but give a more uniform colour to a large surface from the impossibility of further oxidation during manipulation. Hence their use in preparing grounds where a large body of uniform colour is essential. Pyrolignite of iron is largely employed in the preservation of timber.
The manufacture of iron liquors is an important industry in Laura-hire. Elsewhere they are only made for local consumption. The continental liquors are obtained in a more concen trated forra, about three times as strong as the Inane manufacture. They are, however, of very fine quality. The only practical method of testing iron liquors is to try them on cloth against samples of an already known quality.
Iron mordants are probably of ancient use. The first English patent was taken out in 1780 by Flight, who proposed to steep iron in " water drawn from tar or tar oil," and to mix the liquor with starch or gum. In 1782, Boothrnan patented the steeping of iron filings, &c., in water mixed with some such fermentable vegetable matter as barley, wheat, or bran. This was practically the Indian method of yet earlier times.
An ordinary iron liquor will teat as follows : Oxide of iron, calculated as protoxide 6.30 Acetic acid .. 7.20 Sulphuric acid .. 0-80 Tarry matter .. 2 30 Water .. . 100.00 Liquors made from acetate of lime and sulphate of iron usually contain an appreciable quantity of sulphate of lime.