Manual of chemical analysis as applied to the examination of medicinal chemicals : a guide for the determination of their identity and quality, and for the determination of their identity and quality, and for the detection of impurities and adulterations : for the use of pharmaceutists, physicians, druggists, and manufacturing chemists, and of pharmaceutical and medical students . umes of nitric peroxide; by theready decoloration of diluted solution of indigo; by its color-ing pine-w^ood bright yellow; and by deep red or brown com-pounds with ferrous salts. The salts of nitric acid are remarka
Manual of chemical analysis as applied to the examination of medicinal chemicals : a guide for the determination of their identity and quality, and for the determination of their identity and quality, and for the detection of impurities and adulterations : for the use of pharmaceutists, physicians, druggists, and manufacturing chemists, and of pharmaceutical and medical students . umes of nitric peroxide; by theready decoloration of diluted solution of indigo; by its color-ing pine-w^ood bright yellow; and by deep red or brown com-pounds with ferrous salts. The salts of nitric acid are remarkable for being all solublein water. The characteristic reaction of nitric acid w^ith ferrous saltsextends also to the nitrates, when previously acted upon bystrong sulphuric acid. The test is performed either by placinga crystal of ferrous sulphate in the liquid under examination,mixed with concentrated sulphuric acid, or by mixing theliquid with a concentrated solution of ferrous sulphate, andpouring this mixture carefully upon concentrated sulphuricacid in a test-tube, or by pouring it into a conical cylinder andplacing concentrated sulphuric acid below it by means of apipette (Fig. 34), so as to form in either case two supernatantlayers. If a large quantity of nitric acid is present, the surfacesof the crystal, or the line of contact between the liquids, become ACIDA. 93. black; if but a small quantity is present, they become reddish-brown or purple. Volumetric Estimation^ see page 61. Examination: Hydrochloric acid may be detected in the acid diluted withabout five times its volume ofwater, by the formation of awhite precipitate, when testedwith argentic nitrate. Sulphuric acid is detectedin the diluted acid by a whiteprecipitate, when the diluted acidis tested with barium nitrate. Nitrous and hyponitric acidsare detected in the diluted acid,by one or two drops of a very di-lute (1:1000) solutio-n of potas-sium permanganate : their pres-ence is indicated by decoloration. Iod
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