ALUMINA, ACETATES OF.—Acetic acid forms with alumina a series of salts, the exact constitution of which is still somewhat doubtful, but which are all exceedingly valuable in the arts. The sesquiacetate, or "red liquor" of the calico-priuters, is perhaps the most extensively used. It is obtained by mixing solutions of lead acetate and alum, allowing the preparation to cool and settle, and filtering off, or decanting, the clear liquor from the insoluble lead sulphate. Equal weights of alum and acetate may be used, but some makers prefer a smaller quantity of the lead salt. Usually a little chalk, soda ash, or soda crystals is added, in the proportion of 5 to 10 per cent. of the weight of alum, to neutralize the free acid present. lied liquor is also prepared, in a similar way, from mixed solutions of alum and lime acetate, lime sulphate settling out, but the product in this case usually retains a certain amount of the sulphate, which impairs the colour, and makes the cloth finish rough. Sulphate of alumina may be adyantageously substituted for alum. Not only does the sulphs.cetate of alumina give as strong a red liquor as that prepared from ammoniacal alum, but the cost is less. Choice of the materials is, however, governed by the preju dices of the consumer or the purposes for which the liquors are made.
The method of manufacturing a good red liquor is as follows :-50 gallons of acetate of lime liquor marking 24° Tw. are heated up to 60° (140° F.) in a copper pan, and 200 lb. of ammonia alum in a crushed or roughly powdered state are well stirred into it, the temperature being kept up until the alum is thoroughly dissolved. This operation usually takes a couple of hours. About 12 lbs. of ground chalk are then stirred into the mixture, which is allowed to cool and settle. The clear supernatant red liquor is then siphoned off, and should register about 20° Tw. The residue, consisting chiefly of sulphate of lime, retains a considerable amount of the mordant, and should be washed with hot water. Tho washings form a weaker red liquor, or are used to dissolve a fresh batch. The red colour is imparted by mixing with the clear liquor a small quantity of a preparation of lichens. Other good recipes are:—
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90 gals. of acetate of limo liquor at 24° Tw.; 372 lb. of sulphate of alumina ; 34 lb. of chalk ; the red liquor from which marks about 16° Tw.
Or 1132 lb. of boiling water ; 453 lb. of sulphate of alumina ; 379 lb. of acetate of lead ; the liquor from which should stand at 18° Tw.
Or — 150 gals. of boiling water ; 460 lb. of alum (potash alum); 460 lb. of acetate of lead ; giving a red liquor of 12° Tw.
The following gives a good Resist Red Liquor :— 1 gal. water.
5 lb. alum.
n lb. acetate of lead. lb, soda crystals.
Acetate of lead gives more certain results than acetate of lime, as it is usually more to be depended upon in quality, the composition of the lime salt being so exceedingly variable. Ammonia alum is also an article of uncertain constitution, and should only be used when its real value can be ascertained by analysis. The sulphate of lime residue is more difficult to deal with than sulphate of lead, as it is much more bulky, and retains a greater proportion of the mordant, requiring there fore more careful washing. All the materials used should be of the best quality, the presence of iron in the alum being especially hurtful. As far as possible all red liquors should be made for immediate consumption, as they deteriorate when kept.
A very excellent mordant for alizariuc colours is made on the Continent by dismaying precipitated alumina in glacial acetic acid. This method has been adopted occasionally in this country, but is exceedingly troublesome. Upon the whole, the crude pyroligneous is the best form of acetic acid for red liquor manufacture, as its very impurities help to give a certain stability to the compound by retarding oxidation.
A good English red liquor will contain from 3 to 5 per cent. of alumina, and the amount of dry acetic acid should be equal to twice the weight of alumina. The constitution of the liquors, however, varies very much with the particular localities and circumstances. Alumina mordants aro excessively sensitive, and cure must be taken not to heat the cloth too strongly alien drying, or else only variable shades of colour are produced. This is especially the ease when the mordants are used in a dilute state.