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out bluestone. When the two were used simultaneously, the amount was so small that the effect could not be appreciated. At the time referred to it was a maxim among millmen that no benefit was to be derived from the use of chemicals. Mr. Küstel, in his book on the Washoe process, after giving a list of different chemicals employed or recommended-none of which were probably ever largely adoptedexpresses strong doubts as to the efficacy of any or all chemicals; and in a later article, after admitting the extraordinary effects obtained on slimes, states that the same process would not be applicable to sands. So much to vindicate the practical originality of this process. It will be shown further on that it can be applied with equal advantage to the working of sands and tailings. There is no certainty as to the formula in obedience to which the chloride of copper-which is formed by the mutual action of salt and sulphate of copper-effects its purpose. Chemists are not agreed as to the various re-actions, and the subject is still under dispute. Its theoretical comprehension is, however, not essential to the practical operations which will be described.

We will first consider the application of chloride of copper to the working of slimes, and, later, its extension to the treatment of sands or pulp.

Slimes constitute the clayey portion of the ore which flows from the battery in wet-crushing mills, and is imperfectly caught or settled in the tanks constructed for the purpose of catching the crushed ore. It is needless to say that with a sufficient number of tanks these slimes could be saved, but lack of space generally renders this impracticable, and the usual plan is to allow them to flow into reservoirs outside of the mill, from which they are afterward dug out, allowed to dry, and hauled to the mill.

The mechanical treatment of.slimes varies but little from that of ordinary ore. Their finely-divided condition renders grinding unneces sary, and calls merely for a sufficiently violent motion to thoroughly incorporate the quicksilver with the pulp.

The length of time devoted to the amalgamation of a charge of ore is influenced to a great extent by the amalgamating capacity of the mill, and by various reasons of economy. It often becomes advisable to sacrifice a certain percentage of the value for the sake of working a greater number of tons per diem. To insure good results a charge should not remain in the pan, subject to the action of quicksilver and chemicals, less than six to seven hours.

In working ordinary ores the quicksilver is not added until the pulp has been thoroughly ground. This is to prevent the flouring of the quicksilver; but since slimes require no grinding, one might suppose that it would be more advantageous to put the quicksilver into the pan on charging, thus allowing more time to the amalgamation.

Experience has, however, shown that better results are obtained by putting in the chemicals, i. e., sulphate of copper and salt, first, and adding the quicksilver from two to three hours later, thus allowing the intervening length of time for the decomposition or "preparation" of the refractory minerals. The reason of this is not immediately apparent, as the quicksilver charged simultaneously with the chemicals should attack the chloridized (?) silver-minerals in statu nascenti. The amount per ton of chemicals employed varies with the richness of the slimes. The quantity is always largely in excess of that called for by the chemical equivalents of the minerals to be acted upon, but in very large pans the relative proportions may be diminished. Taking ordinary slimes, assaying thirty dollars per ton, as a basis, the average quantities

of sulphate of copper and salt employed per ton are 10 to 12 pounds of the former and 20 to 25 pounds of the latter.

These quantities may be advantageously increased on slimes of higher grade. The exact amounts must be determined by conscientious assays. In working slimes of uniform character, the varying fineness of bullion furnishes an excellent empirical test of the amount of chemicals to be employed. The baseness of the bullion increases with the quantity of sulphate of copper used, owing to the precipitation of copper by the iron of the pan, and its consequent amalgamation. The millman soon discovers that beyond a certain point an excess of sulphate of copper produces no adequate results besides reducing the fineness of his bullion. Having once determined the average fineness of his bullion when working under the most favorable circumstances, he increases or diminishes the amount of sulphate of copper as the bullion becomes finer or baser than his standard.

The same amount of chemicals with richer slimes will produce finer amalgam, which is due to the fact that a larger amount of silver is amalgamated while the same percentage of copper is precipitated. Should the value of the slimes and consequent fineness of the bullion increase materially, it becomes necessary to determine by assay the most advantageous proportion, and to adopt a new standard of fineness. A source of great expense in the working of slimes is the excessive and apparently unavoidable loss of quicksilver. Working with all the advantages of settlers and agitators, this loss seldom falls below four pounds per ton, whereas in quartz-mills it does not as a rule exceed 14 to 11⁄2 pounds per ton of ore. This is undoubtedly due to the nature of the slimes, which have the same effect upon the quicksilver as oil or grease, forming a film or coating over the surface of the metal, and preventing the globules from uniting. The minute particles settle with difficulty, and to a great extent flow off with the tailings. The excessive loss in working slimes cannot with justice be ascribed to the action of chloride of copper, as in working the tailings by the same process the loss of quicksilver per ton is not greater than in ordinary quartz-mills, thus proving sufficiently that the deleterious action of chloride of copper upon quicksilver is not appreciable upon so large a scale.

Many attempts have been made to effect a saving of quicksilver in milling, but so far only mechanical appliances have met with success. Although sodium, sodium amalgam, cyanide of potassium, &c., are very effective in temporarily "enlivening" the quicksilver, their action speedily dies out after the latter has been transferred to the pan, and experience has sufficiently demonstrated that when employed in practicable quantities they have no effect in aiding the amalgamation. The only thorough method of cleansing quicksilver is to retort it, and the use of proper straining-sacks will render a recourse to the method unneces

sary.

The following table will show results obtained in working on a large scale two different lots of slime:

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The results obtained in the working of lot No. 2 are somewhat above the average, which can be estimated at about 80 per cent. of the assay value.

The method of treatment now in vogue is susceptible of modification and improvement. The yield can be increased by charging the chemi cals at two different periods, say two-thirds at first and the remaining third two or three hours later. This is due to the fact that the action of the chloride of copper becomes more feeble as time elapses, and is revivified by the addition of this second portion.

A saving in the amount of salt consumed can be effected by dissolving it together with the sulphate of copper in vats in proportions approximating to their chemical equivalents, and charging the resulting chloride of copper in the liquid state. The plan of putting the sulphate of copper and salt into the pan separately, necessitates a large excess of the latter to insure the complete decomposition of the former. An excess of salt was originally deemed advantageous on the supposition that it would act beneficially in holding the chloride of silver in solution, thus presenting more surfaces of contact to the action of the quicksilver, and, moreover, would convert the Hg Cl formed to Hg Cl2, in which state it would be precipitated by the iron of the pans in the metallic form, It is, however, improbable that such re-actions should occur on a large scale where the re-agents represent so small a proportion of the entire mass.

The discovery of a cheap method of working slimes led to important results. The same process was soon applied to the working of low-grade tailings, of which vast quantities had accumulated on the plains bordering on the Carson River, at Dayton, and at other points. Several mills, with a capacity of working from 250 to 300 tons per diem each, are now in operation in Dayton and vicinity. The tailings, which were formerly allowed to run into the Carson River, are now carefully saved, and in fact to such an extent has the re-action set in against the wasteful prac tices of the past, that many mill-owners save the tailings after they have passed through the pans, with a view to reworking them at some future time. The tailings being mostly very poor, it becomes necessary to work a large amount daily in order to obtain a fair interest on the capital invested. This is effected by using very large pans and by rapid amalga mation. Economy in the time devoted to amalgamation cannot, however, be effected without sacrificing a portion of the precious metals which might otherwise be saved. It is, however, considered policy to suffer this loss. The method of treatment is practically the same as in working slimes, with the exception that a smaller proportion of sulphate of copper and salt is used, and that in other respects less attention is paid to the extraction of a high percentage, the value of the tailings not justifying too careful a manipulation. For the same reason the extra expense of grinding the tailings, which would undoubtedly increase the yield, is dispensed with.

As a rule the bullion produced is very base, not exceeding on the average .450. and often going as low as .350.

In the mill of Birdsall & Co., in Dayton, where the crude bullion rarely exceeds in fineness the latter figure, an inexpensive process has been adopted for partially refining it.

As the bullion comes from the retort a great portion of the copper is found in a crust on the surface of the slab. This slab-crust, which contains some silver and gold, is separated from the finer metal beneath, and the latter is cast into bars 500 to 600 fine. The cupreous crust is roasted in a reverberatory furnace and crushed, and the copper-oxide separated by

means of sulphuric acid. The bullion from other mills is sold in the crude state, and suffers a discount proportionate to its baseness.

Even with the use of sulphate of copper and salt the percentage extracted from low-grade tailings rarely exceeds 50 to 55 per cent. This is due principally, as above stated, to the necessity of a cheap, rapid, and consequently imperfect treatment. The same tailings, however, worked without chemicals, but otherwise in the same manner, would not yield over 20 to 25 per cent. of their value, and in some cases not so much as that. Richer tailings give better results, and are also treated more carefully.

In a mill of large capacity, and in good working order, the cost of working does not exceed $3 to $4 per ton. Hence there is still a margin for profit on tailings assaying only $9 to $10 per ton.

The pans now almost universally in use in the Washoe tailing-mills have a capacity of from 6 to 8 tons, and the time of working the charge generally does not exceed four hours. More than half an hour, however, is consumed in charging and discharging, in heating the pulps, &c. The actual time of treatment, therefore, is less than three and a half hours. The following table will show the amount extracted from one half hour to one half hour, from a charge of tailings assaying $15.31 per ton, worked in a pan of eight tons' capacity.

Value of tailings, $15.31.

Assay value of sample from pan, end of first half hour...
Assay value of sample from pan, end of second half hour...
Assay value of sample from pan, end of third half hour..
Assay value of sample from pan, end of fourth half hour.
Assay value of sample from pan, end of fifth half hour..
Assay value of sample from pan, end of sixth half hour.
Assay value of sample from pan, end of seventh half hour...
Assay value of sample from pan, end of eighth half hour...

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Total percentage extracted, 49.30 per cent. The falling off in the yield in the seventh and eighth half hours is due to the insufficiency of chemicals used, their action having spent itself in the earliest part of the treatment.

Until the introduction of the use of the sulphate of copper and salt, the working of tailings was confined to rich lots, where a small percentage of the value would still prove remunerative, and to blanketconcentrations. The richness of the latter consisted to a great extent in amalgam, and its successful extraction was consequently an easy mat

ter.

990 1000

Before dismissing the subject of slimes and tailings, it is necessary to refer to certain classes of these ores which do not yield to the action of sulphate of copper and salt to the extent claimed in the foregoing pages. The precise cause of this rebelliousness has never been accurately ascertained, but from the fact that the bullion produced in working them is always of exceeding fineness ( and over) even when a large excess of sulphate of copper is used, it is evident that the evil consists in the presence of some substance which decomposes the sulphate of copper, thus producing the same effect as if none were used. This injurious agent is probably an alkali or alkaline earth. It is to be regretted that we have no knowledge of any cheap chemical re agent producing practically the same effect as chloride of copper, and which would not be subject to this decomposition.

The following table will show to what extent the treatment of slimes is affected by the elimination of the copper-salt. Five hundred and sixty-two and one-quarter tons of slime from Chollar ore were worked in charges of 2,500 pounds each, with 15 pounds sulphate of copper and 30 pounds salt to the charge. Total amount worked, 562 tons.

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Within half an hour of putting the sulphate of copper into the pan, chemical tests could not detect the presence of copper in solution in the pulp, thus proving that it had been almost immediately decomposed. The same phenomenon has presented itself in the working of tailings. Such cases, however, are exceptional, but prove why in certain instances the use of sulphate of copper and salt may not produce the effects claimed for them. Apart from these exceptional cases the beneficial effects of chloride of copper being thoroughly established, the question naturally arises why its use is principally limited to the working of slimes and tailings, and why it is not more generally employed in quartzmills. There is not the slightest doubt that an intelligent use of chemicals would prove highly beneficial in many cases where the old method of treatment without chemicals is adhered to. The ores of the Comstock ledge are particularly docile under their influence. It is true that many mill-men claim to have investigated the matter, and have pronounced against the use of chemicals, but, as has already been stated, their experiments were carried on in such an unfair manner that failure was inevitable. It could not be expected that a few ounces, or even a few pounds, of sulphate of copper and salt would produce appreciable results upon a ton of ore, and yet mill-men were deterred from using larger quantities through the fear of producing baser bullion. It is a common superstition that fine bullion is a guarantee of skillful amalgamation, than which nothing is less true. Until this prejudice is eradi cated it is useless to look for the employment of sulphate of copper in quartz-mills in quantities sufficient to establish its merits. Another cause of indifference on the part of Washoe mill-men is the fact that they generally find no difficulty in returning by their present method of working 65 per cent. of the value of the ore, the amount universally guaranteed by customs mills, and are, naturally enough, not disposed to increase the cost of working without corresponding benefit to them selves. The mine-owners also appear to be satisfied with these results, but their apparant indifference to their own interests does not admit of so simple an explanation.

The first quartz-mill to adopt the use of sulphate of copper and salt was that of the Meadow Valley Company, near Pioche, Nevada. This mill commenced operations in the summer of 1870. Owing to a misunderstanding only a small supply of sulphate of copper was on hand at the time, and when this was exhausted the difference in percentage extracted was immediately apparent. During the first week's run the yield was equal

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