200. The so-called chlorination assay, is so far incorrect that it gives not only the silver chloride, but all other silver compounds which are soluble in solutions of the alkaline or earthy hyposulphites It may seem that this is a matter of indifference, since all the silver that can thus be extracted can be obtained in the large operation, and this view is correct as to the silver sulphate.

But, in roasting silver ores, if all the requisites of a thorough chloridation are not present, certain compounds of silver are formed, which, though soluble in hypo (or in hot brine), and therefore extracted in the ordinary chlorination assay, are neither chloride nor simple sulphate. These compounds render the extraction of the silver more difficult, and affect the purity of the resulting bullion, whether the leaching process, or amalgamation be employed.

As ammonia dissolves the chloride and sulphate, but not the compounds alluded to, I suggest that comparative assays be made, occasionally, with hypo and with ammonia, as the solvents.

The following account of some investigations, made in 1876, and published at the time in the Mining and Scientific Press, will assist in explaining this matter:

B. Rewashed with hot water; filtrate contained neither chlorine nor heavy metal.

C. Again washed, with cold solution of sodium hyposulphite; filtrate tested with potassium sulphide gave a copious brown precipitate containing silver, lead, arsenic, iron, etc.

D. Excess of potassium sulphide was added to filtrate C, and afterwards, to prevent re-solution of arsenic, iron protosulphate in slight excess, then nitric acid to decompose the hyposulphites. A white precipitate was slowly formed, which on boiling became yellow (sulphur).

E. - Precipitate from D, removed by filtration, and filtrate treated with an acid solution of silver nitrate, gave no precipitate.

The inference is, that the metal salts contained in the washed tailings, and dissolved by solution of sodium hyposulphite, were not chlorides.

4. - Sample of amalgamation tailings containing silver, per ton...................... $4.00

A. Washed on filter with hot water; filtrate tested with barium nitrate showed the presence of a sulphate. Washing continued until no more sulphate could be detected.

B. Washing repeated with hot solution of sodium chloride (free from sulphate); a portion of the filtrate tested with potassium sulphide, gave a copious pecipitate; the remainder tested with barium nitrate also gave an abundant precipitate.

The inference is that the metal salts extracted by sodium chloride were sulphates, and as the silver is extracted by hot brine about as perfectly as by sodium hyposulphite, it seems probable that the metals exist as a multiple sulphate, otherwise the silver sulphate would have been extracted by hot water alone. The tailings gave no appreciable silver chloride by treatment with ammonia. The metals extracted by hot brine are very slowly reduced by metallic iron, so that a good result is obtained from ore in this state, in pans, only by long continued working, and a base bullion is obtained, while the addition of lime to the pulp, intended to produce finer bullion, entirely prevents the reduction, causing richer tailings. With silver chloride, even a great excess of lime does not impede reduction, nor prevent amalgamation, though the latter is somewhat impeded. By longer roasting of the ore, the formation of silver chloride was improved, but the ore required an addition of sulphur, in some form, to give the best attainable result.