AMALGAMATION IN BATTERY.

Frequently, when the gold in the ore is fine, and sometimes also when it is coarse, the plan of battery amalgamation is preferred. By this mode mercury is introduced into the battery, a small quantity being sprinkled in upon the feed side at intervals of from half an hour to two hours, as may be needed-the quantity of mercury required in the battery varying with the richness of the ore and the fineness of the gold; the average amount being about an ounce of mercury for every ounce of gold obtainable from the ore. If the gold be very fine, more is needed-in practice, the quantity being judged of by the appearance and consistence of the amalgam formed. The amalgam in the battery should be too hard to be readily impressible with the finger, and yet not so dry as to become brittle, which might cause it to break up and be thrown out in little pellets through the screen. A small portion of the mercury is thrown out, which, with the gold it catches on its way, forms a little ridge of amalgam on the copper plate, generally placed under the lip of the mortar outside the battery. This amalgam should be of such a consistence that an impression can be made upon it with the finger, and yet not too easily. If the amalgam becomes too soft, no more mercury is added till it regains its normal condition; and, on the other hand, if it becomes too dry and hard, the supply is increased until it is brought to the proper consistence.

For the purpose of collecting the amalgam formed in the batteries, the latter are usually partly lined with plates of sheet copper. Upon the surface of these plates the amalgam collects, not in a layer of uniform thickness, but in irregular bunches and little ridges, the position and thickness of which are mainly dependent upon the "swash' produced in the battery by the order in which the stamps fall. The curious effects of this "swash," in determining the distribution of the amalgam upon these plates, is a point worthy of more attention, perhaps, than it has yet received.

Below the batteries come the sluices, with their copper plates, riffles, etc., for saving the gold escaping from the former; these arrangements, differing generally but little from such as are used in the Grass Valley system; the blankets and their accompaniments, however, being but rarely used where amalgamation in battery is practiced.

Various opinions are entertained by metallurgists and millmen as to the efficiency and economy of battery amalgamation; some, who have practiced it for years still adhering to it, satisfied with their experi

ence, and, while it is no doubt open to certain objections, it is preferable to all others. Quartz mills usually run steadily both day and night; where, however, battery amalgamation is practiced it becomes necessary now and then to stop the mill for a "clean up"--that is, to collect the amalgam, which has accumulated in the batteries and on the copper plates. Sometimes the whole mill is stopped for this purpose, while at others, in order to save time, a single battery only is stopped and cleaned up, and then another, and so on, till the whole are thus gone through with. A "run" in a quartz mill varies, according to circumstances, from twenty to sixty days. The amalgam obtained is strained and retorted in the manner already described.

For the purpose of extracting free gold from quartz, the ore is rarely reduced to any finer state of pulverization than is attained by crushing under the stamps with the screens already described. But when auriferous sulphurets are present, sufficiently rich in gold to make its extraction an object, they are frequently subjected to a further process of pulverization and amalgamation. This is effected by grinding them in a flow of water and mercury in an arrastra, Chili mill, or in some of the many patent cast iron pans or grinding mills of recent invention. These pans having first been introduced as a substitute for the German barrel in working the silver ores of Nevada, where they still continue in use, were afterwards employed also for working the gold ores of this State; and, although they may in certain cases be used here to advantage, especially in treating such mercurial residues as may be collected from the various parts of a quartz mill, they are nevertheless gradually going out of use, many millmen having discarded them altogether. For a description of these pans, and further information touching the extraction of gold from the sulphureted ores, Küstel's recently published work on Concentration and Chlorination may be consulted to advantage.

THE MARIPOSA PROCESS.

This process, so called from its having been first introduced at the Benton mill, on the Mariposa estate, consists in reducing the ore to an impalpable powder, by placing it, previously crushed to a coarse sand, together with a quantity of chilled, half-inch cast iron bullets, in a large horizontal revolving cylinder, or cask of wrought iron, thorough pulverization being effected by the friction of the rolling balls. From this "ball grinder," as it is called, the ore is conveyed to a strong airtight iron chamber, where it is subjected to the action of the vapor of

mercury, volatilized by means of superheated steam.

When the amal

gamation of the gold is supposed to be complete, the apparatus is suffered to cool down, and the pulp having been discharged into a receiver beneath, is then washed upon a long copper shaking table, to collect the amalgam formed. This process, so far as tried, has worked remarkably well, though the question of its general economy can hardly be considered settled.

CONCENTRATION.

The concentration of ores is a subject of importance in California, chiefly in so far as it relates to the separation or extraction of auriferous sulphurets from the mass of ore, of which they usually constitute not more than one or two per cent., the proportion sometimes being much larger. Notwithstanding its great practical importance, the concentration of sulphurets has hitherto received but comparatively little attention in California. At Grass Valley, and in some other localities, they are saved, to a certain extent, to be subsequently worked by the chlorination, or some other process. For this purpose settling boxes are usually employed, to catch the heavier sand, which is afterwards worked over in a sluice, the cradle or rocker being sometimes used to finish up the work. the work. At Grass Valley, recourse has in a few cases been had to a Cornish round buddle, while a variety of patent concentrators have, to some extent, come into use in different parts of the State.

Of the latter, Hendy's concentrator, in its improved form, is believed to be one of the best. This valuable machine, which is designed for separating the finely comminuted quicksilver, amalgam and gold from the refuse matter and collecting the same, as well as for concentrating and saving the sulphurets, operates through a combination of centrifugal force and gravitation-the only principles, as experience has shown, capable of effectually accomplishing this object. Of late this concentrator has been coming into very general use, it having been introduced into many of the leading mills of Grass Valley, at Virginia City, and elsewhere in the State of Nevada; in Arizona, Mexico, Australia, and most other prominent gold and silver producing countries, giving the most unqualified satisfaction wherever tested. But few of these machines, however, are yet based upon a thorough comprehension of the whole subject, inasmuch as they are incapable of yielding under varying circumstances the best attainable results-this question of the concentration of ores being one beset with many inherent difficulties. The problem to be solved can, indeed, be easily stated, since the object to be obtained consists simply in effecting as complete a sep

aration as possible of the particles of ore, according to their different specific gravities. But this, where a large mass of material, consisting of irregular particles of all shapes and sizes, from the coarsest sand to the most impalpable slimes, cannot well be accomplished in a single operation.

While much that is useful may be learned from what has been achieved in continental Europe, it is not to be supposed that everything found to answer well there can be adopted without modification here with equal chances of success, inasmuch as the circumstances are widely and often vitally different; still, many valuable hints, together with much that is capable of direct and advantageous application, have been derived by our metallurgists from the greater scientific knowledge and experience of the Old World.

PLATTNER'S CHLORINATION PROCESS.

This process, which has been in use at Grass Valley, Nevada county, for several years past, is the only method yet known by which the auriferous sulphurets of California can be cheaply and economically worked upon a large scale; more than ninety per cent. of the gold they contain being obtained by this method. It is now ten years since the chlorination of auriferous sulphurets was first successfully introduced at Grass Valley, and yet there are scarcely more than half a dozen of these establishments in the State outside the limits of that place and the adjacent town of Nevada, so frequently are processes of real merit overlooked and neglected, while those of doubtful utility are liberally patronized.

It is now, however, becoming generally known, that auriferous sulphurets, containing but little silver, can be readily worked to within less than ten per cent. of the fire assay, at an expense of considerably less than twenty dollars per ton. The outlines of the method by which this result is effected being briefly as follows: the concentrated sulphurets are first subjected to a complete and thorough oxidizing roasting, with constant stirring, upon the hearth of a reverberatory furnace, for a length of time varying from twenty to twenty-four hours, according to the condition and character of the ore. In this roasting there are two distinct periods, viz: the first, or oxidizing, and the second, or final period, in which the various metallic salts formed during the first are again decomposed. During the first period the temperature employed is moderate, the ore being kept at a dark red heat only. After the requisite temperature is once reached, comparatively little

fuel is required, since the ore itself soon begins to glow, and from this time on, the burning sulphur contributes largely towards maintaining the heat of the furnace.

The most important chemical changes occurring at this stage are the following the sulphurets are gradually decomposed by the oxygen in the heated stream of atmospheric air constantly passing over them; the sulphur is oxidized, the greater portion of it burning only to sulphurous acid, which passes off in the gaseous form; and the metals, originally combined with the sulphur, are also oxidized, a portion to the state of protoxides only, while a portion passes to the state of sesquioxides. The sulphur, however, does not all pass off as sulphurous acid, a considerable portion of it being still further oxidized to sulphuric acid, which combines with a portion of the metallic protoxides. During this period the ore, as it is stirred, constantly exhibits the blue flame peculiar to burning sulphur, throwing out brilliant sparks, produced by the rapid burning, in the heated air, of minute particles of undecomposed pyrites.

When the series of changes above indicated are nearly complete, the evolution of sulphurous acid greatly diminishes, the blue flame and the sparks disappear, and the furnace exhibits a strong tendency to cool down, calling for an increase of fuel, which, being added, the second or final period begins with the resulting increase of heat. The temperature being now raised to a bright red heat, the metallic sulphates formed during the first period are mostly decomposed, the sulphuric acid yielding a portion of its oxygen to the protoxides which pass to the state of proxides, while the sulphurous acid produced is driven off. Thus, at the end of the roasting, if it be properly conducted, and only sulphurets are present in the ore, there remain the oxides of the metals alone with a certain quantity of sulphate of lead, (which is not decomposable by heat alone,) in case that metal is present. Arsenic and antimony, if present, behave very much like sulphur, except that they have a stronger tendency to form arseniates and antimonates, and that the salts so formed are much more difficultly decomposed by heat than is the case with the sulphates, so that a portion of them is always found in the residue, while the quartz remains unchanged. The alkaline earths, if present, are chiefly converted into sulphates, which are undecomposable by heat. But as some of them, especially lime and magnesia, have a tendency in the subsequent operation to absorb chlorine uselessly, and to produce some other undesirable effects, the theory of which has not yet been very well investigated, the roasting is sometimes, during the latter period, in case these earths are present,