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.

After this a third specimen was received from Huelgoeth; it was very small, but as rich as the foregoing, and in it there were distinguishable, besides granular cubic crystals of chloride of silver, other grains of an olive-green color, which had exactly the same appearance as the bromide had. Plateros and the following experiments proved the presence of the substance.

Five grammes of the pulverized mineral were boiled in a solution of oxalic acid, until the oxide of iron was perfectly dissolved: the residue weighed about a gramme, and it evidently contained a mixture of canary-yellow and white grains. It was digested in hot solution of ammonia until all the yellow powder disappeared; it required a large quantity of the alkali for this purpose, which would not have been the case to dissolve pure chloride. The solution was gradually saturated with nitric acid, and it was observed that the successive deposits formed had an evident yellow tint, but gradually diminishing in intensity, except the last, which were white. The yellow deposits were collected and examined in the following manner:—A portion was treated with chlorine and æther; the æther became of a yellow color. Another portion was dissolved in ammonia, hydrosulphate of ammonia was added to the solution, and the black precipitate formed was separated, and was found to be pure sulphuret of silver. The liquor was concentrated by exposure to the air, and filtered to separate the sulphur which was deposited; a little potash was then added, and it was evaporated to dryness; acetic acid was added to saturate the excess of potash, and it was again dried.

To determine whether the saline residue contained a bromide, a small portion of it was treated in a tube with pure nitric acid, and a yellow liquid was immediately obtained. Another portion was mixed with peroxide of manganese, and the mixture was placed in a glass tube; a few drops of concentrated sulphuric acid were added, and when gently heated, red vapors were immediately disengaged, and alter some lime there were deposited on the sides of the tube small drops of a red liquid. The existence of bromine was therefore evident, and it was proved that the bromide was unmixed with iodide. Bromide of silver appears to be rare at Huelgoeth; but it may be readily distinguished from the chloride by its greenish or canary-yellow color, which is characteristic of it. It is remarkable that it occurs with the chloride in the same specimens, but without there being an intimate mixture of the two substances.

The Daguerreian Journal.

NEW YORK, MARCH 1, 1851.