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,

converted into a chloridizing roasting by the introduction of a certain quantity of common salt into the furnace, which is found to obviate the difficulty. When the roasting is complete the ore is discharged from the furnace and allowed to cool. It is then damped with water to the proper degree (it should be only damped, not wet) and sifted into a large tub or vat-the chloridizing vat,—provided with a false bottom, on which rests a filter composed of broken quartz and sand. The inside of this vat is covered with a coating of bitumen, or other impervious material not attacked by chlorine, in order to protect the wood. The vat is provided with a close fitting cover, which can be luted on and made air-tight. The ore being placed in the vat, chlorine gas is now generated in a leaden vessel by means of sulphuric acid, common salt and binoxide of manganese, and after being conducted through a vessel of water, in order to free it from chlorhydric acid, which, if allowed to pass into the ore, would produce a series of undesirable effects, is conveyed by a leaden pipe to the bottom of the vat. Here it gradually accumulates and rises through the ore. But as it is some time in reaching the top of the vat, the chlorine is generally admitted at the bottom, in order to save time, before all the ore is introduced, and the latter is then gradually sifted in as the chlorine rises.

When the vat is filled and the gas makes its appearance at the top of the ore, which may be known by its greenish-yellow color, as well as by its suffocating odor, the cover is placed over the vat and luted tight. The chlorine is still allowed to enter the vat until it begins to escape through a small hole in the cover, left open for the purpose. The supply of gas is then shut off, the hole in the cover stopped and luted, and the whole allowed to stand for twelve or eighteen hours, to complete the chlorodizing of the gold. Water is then introduced, which absorbs the chlorine and dissolves the chloride of gold formed. The solution is drawn off from the bottom of the vat, a small stream being permitted to run in constantly at the top till the lixiviation is complete. The residue in the chloridizing vat is then thrown away, while the solution obtained, which is precious, as it contains all the gold, is conducted to the precipitating vat or vats.

The chlorine gas employed in this operation is suffocating and poisonous if inhaled, and great care should be taken not to permit it to escape within the building. But there is little danger of sudden death from inhaling chlorine, since a few whiffs of this gas will serve as a sufficient admonition to greater caution.

To the solution of chloride of gold in the precipitating vats is now added a solution of protosulphate of iron, which precipitates the gold

in the form of impalpably fine metallic powder. The solution is permitted to stand for some time, usually over night, in order to afford time for the precipitated gold to settle completely. The water is then carefully drawn off, the precipitated gold collected upon a large paper filter, carefully dried, and then melted and run into bars. The gold bars thus obtained, when the work is properly conducted, are .999 fine.

In practice, this process requires careful attention in all its various details, both in the roasting and in the subsequent chloridizing and precipitation of the gold. The presence of silver in any considerable proportion requires, moreover, important modifications of the process. But where only gold is present in the sulphurets, there is little difficulty -none but what can be readily managed by any one who has a fair comprehension of the general principles of the chemistry involved.

As stated, almost the only means yet adopted in California for pulverizing auriferous quartz, is the stamp, employed in the manner already described. Various other modes of crushing have been devised, but none of them have ever been extensively adopted, and it is difficult to foresee by what implement or mode the stamp is to be hereafter superseded, if any. In this connection it may be observed that the style of the California stamp and battery arrangement is in advance of that of any other country; while the means here employed in the best mills, to extract and save the gold, compares favorably with those anywhere in use. But many of the mills in California are still very imperfect in their gold saving appliances, the loss of the finer portions of the metal in the tailings being large.

In the treatment of sulphurets the same is true, though perhaps in a less marked degree; and it may be anticipated that the chlorination process, as it comes to be more widely known and better appreciated, will contribute largely to induce the employment of better and more systematic methods of concentration, the whole securing such economy in saving the precious metal, that a much lower grade of ore will soon be profitably worked than is practicable at present.

In view of the many novel experiments being made, and the new inventions seeking recognition by the mining public, it may be said that the employment of new modes and machinery promises, perhaps, less certain success than an adherence to the old, if only it be used with the requisite degree of intelligence and care.

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CHAPTER X.

MINES AND MINING.

Rapid Exploration of the Placers-Overestimate of Earnings-Chances Still Good-Improved Conditions-Northwestern Counties-Character of Mines-Gold Beaches, etc.--The Central Districts-Various Branches of Placer Mining-Quartz Mining-Number of Locations-Early Efforts-Present Results-Mining at Grass Valley-A Representative Mine-Butte, Sierra, and Plumas Counties-Gold Bearing Slates and GossansAuriferous Cement and Gravel Beds-Openings for Enterprise, Labor, and CapitalSilver-Iron-Quicksilver-The New Almaden Mine-Mineralogy of the Pacific Coast.

As the discovery of gold was the cause that led to the rapid populating and permanent settlement of California, so has the business of mining for that metal since formed the leading pursuit of its inhabitants. For six or eight years after that event, this occupation, in which more than three fourths of the adult population of the State were engaged, was prosecuted almost solely on the bars and along the banks, or in the beds of the rivers and gulches, and upon the alluvial flats that constituted the more superficial placers. During that period this branch of mining advanced from a very crude and imperfect, to the highly efficient and somewhat complicated system now in vogue; and which, in most localities, renders the exercise of some little skill, and the employment of at least a small amount of capital, essential to

success.

Of the various improvements thus from time to time introduced, it may be observed, that they were less the result of a provident foresight than of a steadily increasing necessity growing out of the gradual impoverishment of the richer and more accessible placers, whereby the employment by the miner of labor-saving machinery and processes became imperative, if he intended to maintain anything like his former rate of earnings. These new modes and devices, thus necessitated, multiplied in the ratio that the more superficial diggings became exhausted, compelling the washing of larger quantities of auriferous