Improvements in the Manufacture of Sodium and Potassium Chromates and Bichromates.

摘要

5057. Spence, F. M., Spence, D. D., [trading as Spence & Sons, P.], and Shearer, A. March 16. Sodium and potassium chromates and bichromates. -A mixture of powdered chrome ore, sodium or potassium hydrate or carbonate, and calcium hydrate or carbonate is heated in a furnace in presence of atmospheric oxygen, the proportion being regulated so that there is sufficient alkali to form monochromate with one half the chromic acid and an excess of lime over that required to form calcium monochromate with the remainder. The frit obtained is reduced to a fine state of division, and is transferred, mixed with water, to a carbonating -vessel, wherein it is subjected to carbonic acid (which may be purified lime-kiln gases), and ammonia or ammonium carbonate. Any ammonia which escapes is collected. The chromate solution is separated from the residue, and heated or concentrated in closed vessels, whereby ammonia escapes and is collected for re-use, and sodium or potassium bichromate forms. The impurities which salt out are removed, and the solution concentrated to dryness or crystallized out.