The solution yields, with hydrochloric acid or soluble chlorides, a white, curdy precipitate of argentic chloride; with hydrogen sulphide, a brownish-black precipitate of argentic sulphide; with the alkaline hydrates a grayish-brown precipitate of argentic oxide, readily soluble in ammonia-water; with the alkaline carbonates, a pale yellow precipitate of argentic carbonate; with sodium phosphate, a bright yellow precipitate of argentic phosphate; and with potassium chromate, a brownish-red precipitate of argentic chromate, all of which are soluble in nitric acid or ammonia-water. From a solution of argentic nitrate many of the metals effect the separation of metallic silver; such are lead, tin, cadmium, zinc, copper, mercury, and also bismuth, arsenic, and antimony.

Examination:

In the employment of argentic nitrate for surgical, ophthalmic, and similar purposes, it is desirable to overcome its brittle properties, and to impart thereto greater solidity, or to modify to some extent its action. This is attained by fusing the argentic nitrate with definite proportions of argentic chloride or potassium nitrate, and such admixtures are officinal in some pharmacopoeias, Argenti Nitras Fusus, and Argenti Nitras Dilutus, U. S. P.; the former containing about 5 per cent. of argentic chloride, and the latter 50 per cent. of potassium nitrate. The Argentum nitricum cum kali nitrico of the Pharm. German. is a mixture obtained by fusing 1 part of argentic nitrate with 2 parts of potassium nitrate.

Such admixtures are indicated in the fused silver salt, by an alteration of its appearance, which is less translucent, whiter, and without the distinct radiate crystalline structure of pure argentic nitrate.

Among the methods of detecting such admixtures, the following are the readiest and most practicable ones:

Potassium Nitrate.-1. A concentrated aqueous solution of argentic nitrate is dropped into ten times its bulk of strong alcohol; if potassium nitrate be present, it will separate after a while in small, white granules, as it is far less soluble in alcohol. Sodium nitrate, which, however, on account of its hygroscopic character, is not adapted to this purpose, cannot be detected by this test, since it is more soluble in alcohol.

2. A small quantity of a dilute solution of argentic nitrate is completely precipitated with diluted hydrochloric acid; the liquid is then warmed, and must, in the case of pure argentic nitrate, when filtered, leave no fixed residue upon evaporation; such a residue would indicate alkaline nitrates or other impurities, the amount of which may be quantitatively estimated by repeated evaporation with a little dilute nitric acid, finally drying the residue at 100° C. (212° F.), and determining its weight, or by ascertaining the amount of dry argentic chloride which is yielded by a weighed amount of the salt.

3. A number of larger and smaller crystals are mixed and broken in a mortar; a small portion of the coarser powder, or fused argentic nitrate, if this be tested, is fused and completely reduced on charcoal before the blow-pipe (Fig. 97): a slight re

FIG. 97.

ticular metallic coating will remain behind, and some alkaline carbonate, if potassium or sodium nitrates were present; they will be recognized by the alkaline reaction, when moist, red litmus-paper is pressed upon the spot of the coal where the fusion took place.

Argentic chloride is indicated, as stated, by a white turbidity of the solution of argentic nitrate; its identity

may be ascertained by its dissolving upon the addition of ammonia-water, but remaining insoluble in nitric acid.

Copper and iron may be detected by completely precipitating the aqueous solution of the salt with hydrochloric acid, and by subsequent approximate neutralization of the filtrate with ammonia-water; this solution is then tested with a few drops of a solution of potassium ferrocyanide; a red precipitate would indicate copper, a blue one, iron; copper may also be detected, or its presence confirmed, by dissolving a small quantity of the argentic nitrate in a little water, in a test-tube, and subsequently adding to the solution a few drops of ammonia-water; an ensuing blue coloration would indicate copper; a white turbidity, lead or zine, which, in the case of zinc, disappears upon the addition of an excess of ammonia-water.

Lead and bismuth, as also foreign metals in general, may be detected by completely precipitating the silver from the aqueous solution of the argentic nitrate by means of hydrochloric acid, washing the precipitate well with water, subsequently testing the filtrate with hydrogen sulphide, and, after again filtering, if necessary, and supersaturating with ammonia-water, testing with ammonium sulphide; a coloration or precipitate in either case will indicate contamination with foreign metals. Lead may also be specially tested for by adding to a solution of 1 part of argentic nitrate in 10 parts of water, 4 times its volume of dilute sulphuric acid; a white precipitate will indicate the presence of lead.

Nitrous acid or argentic nitrite, traces of which are frequently met with in the fused argentic nitrate, and which are more considerable in amount in proportion to the extent of the admixture with potassium nitrate, will be indicated by a slight turbidity upon dissolving the salt in water, and readily recognized as fol

lows: A dilute solution of the salt is completely precipitated by the addition of a slight excess of hydrochloric acid, rapidly filtered, and the filtrate added to a solution of potassium iodide, containing a little mucilage of starch; if nitrous acid be present, a blue coloration will be immediately produced.

Estimation:

The determination of the purity of crystallized argentic nitrate, as also the amount of the latter salt when associated with argentic chloride, potassium nitrate, or other substances which may be used as admixtures or for the purpose of adulteration, may be readily accomplished either gravimetrically or by the method of volumetric analysis.

I. Gravimetric.-One gram of the salt is dissolved in a small amount of water, the solution filtered, if necessary, and hydrochloric acid subsequently added until a precipitate ceases to be produced; the precipitate is collected upon a tared filter, thoroughly washed with water, and finally dried at 100° C. (212° F.) until of constant weight. If the salt be pure argentic nitrate, the precipitate of argentic chloride thus obtained will weigh 0.8441 gram; if it be argenti nitras fusus, it will weigh 0.801 gram, and if argenti nitras dilutus, 0.422 gram, respectively.

II. Volumetric.-About 0.5 gram of the salt is dissolved, in a beaker, in about 20 cubic centimeters of water, a few drops of a solution of potassium chromate added, and subsequently a decinormal solution of pure sodium chloride (containing 5.85 grams of the dry, crystallized salt in 1 liter) allowed to flow into the liquid from a burette until, with constant stirring, the red coloration of argentic chromate remains permanent.

One cubic centimeter of the decinormal sodium chloride solution corresponding to 0.017 gram of pure argentic nitrate, this number, when multiplied by the number of cubic centimeters employed, will indicate the amount of pure argentic nitrate in the specimen under examination.

ARGENTI OXIDUM.

ARGENTUM OXYDATUM.

Oxide of Silver. Argentic Oxide.

Ger. Silberoxyd; Fr. Oxyde d'argent; Sp. Oxido de plata.
Ag2O; 231.4.

An olive-brown, amorphous, odorless powder, which, when heated at a temperature of from 60 to 80° C. (140-176° F.), becomes almost black; at 250° C. (482° F.) it begins to decompose, and at 300° C. (572° F.) it loses the whole of its oxygen,

leaving behind spongy metallic silver; it is also gradually reduced by solar light.

Argentic oxide is sparingly soluble in water, one part requiring about 3000 parts for solution, but is freely dissolved by ammoniawater, as also by warm, concentrated nitric and sulphuric acids; it is insoluble, however, in the fixed alkaline hydrates. Its aque ous solution has an alkaline reaction and a metallic taste, and is rendered turbid by a small quantity of carbon dioxide, but becomes clear again upon the absorption of a larger quantity of the gas. When argentic oxide is triturated in a mortar with the sulphide of arsenic or antimony, finely divided sulphur, amorphous phosphorus, tannic acid, and many other readily oxidizable substances, ignition takes place.

The purity of argentic oxide is ascertained by its solubility in ammonia-water, and also in hot nitric acid, without effervescence, and by the fact that the latter solution, when completely precipitated with hydrochloric acid, gives a filtrate which leaves no residue upon evaporation, and yields no reaction with hydrogen sulphide, either in the acid solution, or on subsequent supersaturation with ammonia-water. One gram of argentic oxide when dissolved in nitric acid, the solution evaporated, diluted with water, if necessary, and subsequently completely precipitated by hydrochloric acid, yields a precipitate of argentic chloride, which, when washed and dried, should weigh 1.236 grams.

ARSENII BROMIDUM.

ARSENICUM BROMATUM.

Bromide of Arsenic. Arsenious Bromide. Arsenic Tribromide. Ger. Arsenbromür; Fr. Bromure d'arsenic; Sp. Bromuro de arsénico. AsBr,; 314.3.

Colorless, prismatic crystals, which possess a peculiar (arsenical) odor, and deliquesce upon exposure to the air. The salt has a specific gravity of 3.66. It melts at from 20 to 25° C. (68-77 F.), boils at 220° C. (428° F.), and is completely volatilizable by heat. Arsenious bromide is miscible with a small amount of water, forming a clear solution, from which, upon standing, arsenic oxybromide, As(OH),Br, is separated; in contact with a larger amount of water, it is decomposed with the formation of arsenious and hydrobromic acids. Its aqueous solution, when saturated with hydrogen sulphide, yields a yellow precipitate of arsenic trisulphide; and when heated with diluted nitric acid, it is decomposed with the liberation of bromine, which dissolves, upon agitation with a few drops of chloroform or carbon bisulphide, with a yellowish or reddish-brown color.

ARSENII IODIDUM.

ARSENICUM IODATUM.

Iodide of Arsenic. Arsenious Iodide. Arsenic Triiodide.
Ger. Arsenjodür; Fr. Iodure d'arsenic; Sp. Ioduro de arsénico.

AsI,; 454.7.

An orange-red or purple, crystalline solid, or bright red, shining, hexagonal tables, gradually losing iodine on exposure to the air, and possessing an iodine-like odor and taste. Its specific gravity is 4.39. When gently heated, the salt fuses, and may be sublimed without decomposition; when strongly heated, it is completely volatilized.

Arsenious iodide is soluble in 3.5 parts of water and in 10 parts of alcohol at 15° C. (59° F.), but is decomposed by boiling water into arsenious and hydriodic acids; it is also soluble in glycerin, ether, and carbon bisulphide, and crystallizes from the latter solutions upon evaporation unchanged. From its solution in a relatively small amount of water, upon standing, a compound consisting of arsenic trioxide with arsenic oxyiodide, As(OH),I, is separated, which crystallizes in bright yellow, shining, crystalline lamina.

The aqueous solution of arsenious iodide is of a yellow color, and when saturated with hydrogen sulphide yields a bright yellow precipitate of arsenic trisulphide; when heated with diluted nitric acid, it is decomposed with the liberation of iodine, which dissolves, upon agitation with a few drops of chloroform or carbon. bisulphide, with a reddish-violet or purple color.

Colorless, silky, acicular crystals, or a yellowish-white crystalline powder, without odor, and of a bitter and acrid taste.

When carefully dried, the crystals melt at 112° C. (233.6° F.), and by very cautiously heating, in small amounts, may be partially sublimed; upon more strongly heating they become decomposed with the development of ammonia, swelling and emitting inflammable vapors, and leaving a carbonaceous residue, which is wholly dissipated at a red heat.