When pure, this salt is totally volatilizable by heat; if a small portion on being heated on a piece of platinum foil over a spirit lamp leaves any fixed residue, it is adulterated. It should dissolve entirely in water; if it leaves an insoluble residue it is adulterated. The impurities generally found in sal-ammoniac, are sulphate of ammonia, sulphate of soda, chloride of sodium, and chloride of potassium; neither of these are considered injurious in the bleaching solution. Occasionally it contains lead, iron, and copper. The presence of sulphuric acid may be detected by means of a diluted solution of chloride of barium, added to a weak solution of muriate of ammonia, in water, this will produce a white precipitate, which is the more copious and dense, the less the liquor is diluted. If it contains lead add to a small portion of it, contained in a test tube, a little diluted sulphuric acid, or a few drops of a solution of sulphate of soda (glauber's salt), if the liquid contains lead there will be prevalent a white powder, or precipitate, this powder scarcely dissolves at all in diluted acids, but it dissolves in a solution of caustic of potash: iron, mix a solution of the yellow prussiate of potash with a solution of red prussiate, a few drops of this added to a weak solution of muriate of ammonia will produce a blue precipitate; copper, pour about half an ounce of the liquid in a test tube, and add to it a few drops of liquid ammonia, if copper is present, the liquid will assume a blue color. Sal-ammonia is known by giving out the odor of ammonia when mixed with caustic of potash: when sal-ammonia possesses a brownish color, it indicates the presence of charcoal, or empyreumatic oil; such sal-ammoniac is good for some purposes, but wholly unfit for chemical purposes.
When sal-ammoniac leaves a non-volatile residue, it may contain sulphate of soda. This is the principal cause of failures with the bleaching solution, as the sulphate of soda has a tendency to blacken rather than bleach Daguerreian impressions. The sulphate of soda as well as the chloride of sodium, is often found in unpurified sal-ammoniac to the amount of ten per cent.
When sal-ammoniac contains much sulphate of ammonia, it fuses and sputters before it sublimes; whereas it otherwise sublimes without fusing. When sal-ammoniac, sublimes without residue, but gives a precipitate when its solution is tested with a solution of chloride of barium, it contains sulphate of ammonia; but when it leaves a non-volatile residue, the precipitate indicates sulphate of soda or sulphate of magnesia.
BROMIDE OF SILVER.
NATIVE BROMIDE OF SILVER AND ANALYSES.
M. Berthier says, that in the district of Plateros, seventeen leagues from Zacatecas in Mexico, silver ore is found in two different states; first, native silver; and secondly and principally in a state of combination in small olive-green or yellowish crystals, supposed to be chloride, but which he found to be bromide of silver. According to M. Duport, from whom M. Berthier received these specimens, this substance is not rare in Mexico, but occurs frequently in fine cubic and octahedral crystals.
The specimen examined by M. Berthier was from San Onofe. It was compact, of a slightly reddish gray color; fracture uneven; splendent; penetrated with small cavities, some of which were partially filled with a substance of a dull pale yellow color, and which the miners call oxide of lead; other cavities contain very small imperfect crystals; which are brilliant, and of a pale olive green-color, and have the appearance of chloride of silver. This specimen was very rich, for it yielded 0.0688 of silver, and contained 0.45 of carbonate of lead, which, intimately mixed with quartz and a little oxide of iron, formed the principal portion of the mass.
M. Berthier has also found this mineral among the silver ores of Huelgoeth, department of Finistère in France. Two specimens were obtained by him: the first of these is described as being porous or scoriform, containing white quartz imbedded in foliated hydrate of iron. On the edges of the foliated iron ore the naked eye could distinguish small cubic grains of a pearl-white color, which had all the characters of chloride of silver.
The second specimen had the appearance of compact oxide of iron, containing here and there milk-white quartz; it was throughout impregnated with chloride of silver, which occasionally appeared in the form of very small brilliant crystals. To analyze this mineral, 10 grammes were first treated with ammonia, and heat to dissolve the chloride of silver, and afterwards by boiling hydrochloric acid to dissolve the oxide of iron; this acid also dissolved a certain portion of lead, which probably was in the state of phosphate. The quartzose residue weighed 32.6 grammes: it contained 0.17 gramme of silver, which must have been in the metallic state: the ammoniacal solution gave by boiling and saturation with nitric acid, 1.84 gramme of chloride of silver, which, supposing it to be pure, contained 1.40 gramme of silver, which, added to 0.17 gramme remaining in the quartz, gives a total of 1.57 gramme; a result which differed so very little from that obtained by essaying, as to prove the absence of bromide of silver, and that this was the case was confirmed by additional experiments.