37

a—3

treat the ore economically, on account of the large percentage of silica there was in the ore. The expense of fluxes was so great that the richest of the ores could not be made to pay by this method of treatment. After the failure of the La Monte furnace, Mr. Bailey erected a crushing-battery on the side of the Waitawheta Creek, consisting of ordinary stamps and the wet-crushing process, the crushed or pulverised ore being run into a series of tailings-tanks, twelve in number, eleven of which were used as settling-pits, the tank which had been emptied forming always the end of the series, and as one got filled up with tailings the stuff from the full tank was removed and reground-up in pans, such as Mr. Bailey had been accustomed to use years previously in Mexico. Sulphate of copper and salt were used in the pans, along with mercury and hot water ; but this system of treatment also proved a failure : a fair percentage of the bullion could not be saved, and the cost of treatment— —£1 10s. per ton —was considered too high for the results obtained. Bailey's company then stopped their operations and sold their plant. It may be premised that where sulphide-of-silver ores exist, such as are found in many of the mines at Karangahake, any system where wet crushing is resorted to will prove a failure to extract all the silver, as a large percentage of the sulphides will not settle, but will float away on the surface of the water. The chemical action of sulphate of copper and salt in amalgamation, although these are used largely in America, and are said to produce good results, has not been satisfactorily determined : it is supposed to effect the decomposition of the sulphides and facilitate amalgamation, but the real chemical action is but imperfectly understood. Sonnenschmidt, a German chemist, and Bowering, an English metallurgist, have different theories as to its chemical action. Sonnenschmidt claims that the salt and sulphate of copper react upon each other, and produce sulphate of soda— which is neutral in its action —and chloride of copper. The latter salt acts upon the argentiferous sulphide, and yields chloride of silver, subchloride of copper, and free sulphur. The subchloride reduces a second portion of the sulphide of silver, and causes the formation of an additional amount of silver-chloride, and subsulphide of copper. The silver salt is then attacked by the mercury, and calomel, or subchloride of mercury, is produced, while metallic silver is set free, which combines with the second portion of the mercury as amalgam. On the other hand, Bowering denies that any of the sulphide of silver is chloridized, and asserts that before amalgamation takes place metallic silver is first produced. He claims that chloride of copper in contact with mercury forms the subchloride of both metals. The subchloride of copper in contact with the oxygen of the air is converted into an oxychloride, which in turn acts on the sulphide of silver, and liberates the metal in a free state by oxidizing the combined sulphur. Again, M. Bissler, in his " Metallurgy of Silver," states that, although oxychloride of copper may possibly be found at times, there does not appear to be any decided evidence that such is the case in practical operations, or that it decomposes the sulphide of silver, while other experiments show conclusively that both the chlorides of copper, under favourable circumstances, do chloridize the argentiferous sulphurets. The experiments, however, seem to indicate that the action of the chloride of copper was much more intense than that of the subchloride. The action exerted by these two reagents in the pan would appear clearly to indicate that the benefits derived from their use are partly to aid in converting the sulphide into chloride of silver, and partly to decompose such minerals as are slightly attacked by mercury. The large quantity of iron produced by grinding in a pan tends greatly to produce subchloride of copper almost as soon as the chemical agents are thrown into the pulp. The quantity of salt used by rnillmen in America varies from Jib. to 71b. or 81b. per ton of ore, scarcely any two establishments having the same rule. The quantity of sulphate of copper also varies, according to the ideas of the millman, from Jib. to 31b. per ton of ore. The addition of sulphate without salt has also become a common practice. The opinion of those who work their ore in this way is that it gives a better yield than when mercury alone is employed, particularly when the ore indicates the presence of galena, in which case it is said to quicken the mercury and render it more energetic. Continued experience appears to determine that in working ores containing only a small percentage of lead the quicksilver very soon becomes dull and inactive, or, as it is technically termed, it sickens, and the yield from the pan is consequently low. Sulphate of copper possesses to a certain extent the property of expelling lead from mercury, but not the power of completely driving out the lead, copper being amalgamated, and sulphate of lead formed at the expense of the sulphuric acid of the copper salt. If a concentrated solution of copper-sulphate be allowed to stand on lead-amalgam the action takes place quite rapidly, mercury containing lead acting much more energetically upon the copper solution than when perfectly pure. Another advantage derived from the addition of a small quantity of sulphate of copper is, that mercury under certain conditions, when exposed to the solution, forms a minute amount of copper-amalgam, which causes the metal to act with a greater intensity in the decomposition of the silver-sulphide than when perfectly pure. The whole of this goes to show that the treatment used by Mr. Bailey in his pans was justifiable, and that he possibly would have saved a fair percentage of the bullion if he had crushed the ore dry and then treated it in his pans, the same as is now done by the Waihi Gold- and Silver-mining Company. At all events, it is well known he lost a considerable portion of the bullion by the water, carrying it off, and to this may be attributed the failure. Becently another plant has been erected on the same site where Mr. Bailey's battery stood, at the side of the Waitawheta Creek, by the Crown Company, which is partiaßy formed with English capital. .This plant consists of a stone-breaker and a Lamberton mill, together with Bailey pans and settlers, as well as a large plant erected by^he Cassel Company to extract the bullion from the pulverised ore by dissolving the precious metals in a solution of potassium-cyanide and precipitating them-by zinc,