Diphenylamine as a Qualitative Reagent for Zinc

Abstract

The qualitative separation of zinc from chromium by the systems of analysis in general use requires considerable time. The production of the green cobalt zincate used as a confirmatory test is dependent upon the comparative amounts of cobalt nitrate and zinc present. Properly adjusting these amounts offers considerable difficulty to inexperienced analysts. The employment of diphenylamine and diphenylbenzidine as indicators in the titration of zinc' suggested their utilization in a qualitative test for zinc. A 0.5% solution of potassium ferricyanide and one gram of diphenylamine dissolved in 100 cc. of glacial acetic acid are the solutions used in this test. MethodAfter the separation of the iron and aluminum groups by sodium hydroxide and sodium peroxide, the filtrate containing the aluminum group is acidified with hydrochloric acid, ammonium chloride is added, and the aluminum precipitated with ammonium hydroxide. The filtrate containing the chromium and zinc is acidified with acetic acid and divided into two equal parts. One part is tested for chromium and the other for zinc. To the part to be tested for zinc, five drops of the diphenylamine acetate solution and 5 cc. of the 0.5% potassium ferricyanide solution are added. The immediate appearance of a dark brown, green or purplish-black turbidity indicates the presence of zinc.To test for any zinc that might be carried over into the iron group, the sulfides of zinc, cobalt and nickel are stirred for a few minutes with cold, dilute hydrochloric acid and filtered. The hydrochloric acid solution is boiled until all of the hydrogen sulfide is expelled, sodium hydroxide is added to alkalinity, the solution cooled and one gram of sodium peroxide added in small portions, with stirring. The mixture is boiled to decompose the excess sodium peroxide, cooled and filtered. The filtrate containing the zinc is acidified with acetic acid and the diphenylamine acetate and potassium ferricyanide are added as above.Knop2 states that in the absence of iron salts no coloration is produced by bichromate in a dilute solution of diphenylamine sulfate. This was found to be true only when the amount of bichromate present was small, less than .05 mg. per cc., a blue color being produced immediately if the concentration of bichromate was .05 mg. per cc. or greater. By using diphenylamine acetate instead of diphenylamine sulfate no color 1

A rapid method for the volumetric determination of indium

“…The freshly precipitated indium hydroxide is very gelatinous and difficult to filter (5). Aging or digestion remedies this condition (2).…”

“…These and other investigators found the lamella of mature xylem to be largely soluble in lignin solvents and insoluble in cellulosic solvents, to exhibit staining effects with supposedly specific lignin stains, and to possess optical properties attributive to lignin (2). Although the evidence in favor of chemists' conception of the composition of the lamella preponderates, there are no data indicative of the complete absence of pectic compounds or of an integral lignin content.…”