Having added the necessary proportion of borax and lead to the ground ore, the whole assay is to be mixed, the handle of the spoon serving as a spatula. A cornet of soda paper is now held carefully between the thumb and fore-finger of one hand, the capsule with the assay in the other; its contents are carefully placed in the cornet, and the adhering particles detached by the small brush, and added to the main mixture in the recipients. When this is accomplished, the sides of the upper part of the cornet must be brought together, folded over about a quarter of an inch, and pressed; care must, however, be used in closing it, lest the under part be broken, and particles of ore be lost. This accident will be avoided by keeping the cornet upon the long side of the middle-finger, during the filling process.

The cornet, filled with the assay, is next placed upon a porcelain basin, where it is to remain until required for the experiment,—and if the same substance is to be investigated several times, or various ores are to be examined for silver, they must be weighed and dressed similarly. The operator should remember, that the weighing of the assay must be followed immediately by the dressing with borax and lead, and should different substances be examined, a superscription on the cornets will prevent any mistake. The weighing and dressing is succeeded by,—

The Fusion of the Assay.

This is effected upon charcoal, in the reducing flame. First, a cylindrical cavity, the size of the filled cornet, is bored with the instrument described in the first Section,-page 25, Fig. 24,into a good piece of charcoal, upon its diametrical section, close to one of the edges. In this deepening the cornet is placed, and carefully adjusted, so that it touches on all parts.

A strong reducing flame is now to be directed upon the whole surface nearly of the assay. Although the soda paper becomes carbonized, still this carbon is not destroyed, until the upper part of the borax, together with the particles of ore, are fused; and when this is accomplished, it is impossible to remove them by the current of air. If, after the combustion of the carbon, portions of

the assay appear as liquid scoriæ, mingled with lead globules, the whole must be enveloped in a strong and pure reducing flame. During this operation, a small portion of sulphur, arsenic, antimony, zinc, et cetera, volatilizes, but the greater portion fuses, and coalesces into a bead with the lead, et cetera; while the argillaceous ingredients, with small quantities of the nonvolatile metals, oxidized, unite with the borax, forming scoriæ. Sometimes, when the alloy consists of difficultly fusible metals, the scoriæ appear to be perfectly free from lead, although, in its under part, the substance remains intact; to submit this to the action of the flame, the charcoal must be inclined to the other side, and thus a further flowing action takes place in the cavity, and the sample is reversed.

By this turning, which cannot be spared even with the most easily fusible mixture, the bottom of the soda paper is brought to the upper part of the charcoal, and, as it will be difficultly consumed by a pure reducing flame, the assay should be placed in such a position to the flame, that the recrements are only covered by it where they are not in contact with the soda paper; by observing these directions, atmospheric air accedes, and the cornet is speedily consumed. When this occurs, the whole sample must be again covered by the flame, in order to reduce and reunite with the main bead all traces of lead, which during the antecedent process might have oxidized and combined with the recrementitious matter.

If the scoria which have been enveloped in the reducing flame appear orbicular, perfectly fluid and free from lead, although their position near the bead of lead had changed several times, the operator may infer that they are free from silver also.

During the operation, it is not indispensable to keep the leaden bead wholly covered while the scoria are subjected to the reducing flame, but the temperature must always be sufficiently high to keep the plombiferous globule fluid. However, if, owing to an imperfect reducing flame, it happens that the recrementitious particles spread over the charcoal, presenting small globules of lead, the main bead must be covered wholly by the flame, and, by inclining the charcoal, brought to those parts of the support

where the small ones are visible, in order to combine with them. The assay being treated, as before mentioned, so far that the scoriæ are in full fusion, and free from lead, the reducing must be substituted for an oxidating flame, which must be kept at a somewhat greater distance from the lead globule. By the judicious application of the flame, the volatile metals, together with the sulphur, separate from the lead, and the readily oxidizable ones, as iron, tin, cobalt, likewise a small portion of nickel and copper, combine with the scoriæ, partly as protoxides, and partly as sesquioxides, whereas the greater portions of the nickel, copper, and silver remain with the lead.

After elimination of nearly all the volatile constituents, the lead and also traces of silver rapidly oxidize;-the latter, even in rich ores, is almost imperceptible, and becomes still more insignificant, when the scoriæ containing the oxide of silver touch the hot charcoal, for the greater portion of it is again reduced, and can be made to recombine, by the movement of the scoria with the argentiferous lead globule.

So soon as all volatile ingredients are vaporized, the motion and oxidation of the lead increase rapidly, attended with considerable ebullition of the scoria. By inclining the support, the button, which is generally surrounded with recrements, is brought to a free place, and allowed to refrigerate. After cooling, if the argentiferous lead,-workable lead,-obtained be of a white color, the operation is completed; but if it appears dull or blackish, traces of sulphur are present, and these must be expelled by repeated oxidation. Great care must be taken, in the expulsion. of the volatile ingredients; for, in the first place, the brittleness of an impure workable lead might prevent it from being removed from the scoriæ, without loss of some of the particles; and, secondly, not only because it can with difficulty be cupelled, but particularly, if sulphur remains, a violent motion ensues in the operation, occasioning the projection of some of the metal from the cupel.

If the regulations here laid down be strictly followed, the small lead globules remaining in the scoria will not be perceptibly argentiferous, as they result only from the oxidation of the main

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bead, and reduction of the oxide from the silverless recrements by the carbon. Although the small quantities of silver oxidizing in company with the lead are to be calculated as loss, still they, in comparison to the oxidized quantity of lead, do not surpass the proportion of silver lost in the beginning of the oxidation with the same quantity of lead; as will be shown after describing this operation.

Of substances treated in this manner, the most difficult of fusion are, sulphides of iron, arsenic, some ores of nickel, cobalt, and a species of rohstein, principally consisting of sulphide of iron; whereas other substances appertaining to the same class generally melt readily, even when they contain difficultly fusible earths.

The fusion of these substances is greatly facilitated by roasting on charcoal, a process to which the lead assays are generally submitted, with subsequent addition of the borax and lead necessary. In this operation, the greater part of the arsenic and sulphur volatilizes, and the remainder becomes acidified, combining with the newly formed oxides of cobalt and nickel. By submitting this assay to the inner flame, the oxide of nickel is reduced, the sesquioxide of iron becomes protoxide, and the acids are reduced to sulphur and arsenic. The metallic nickel combines with the lead, together with the silver and traces of sulphur and arsenic, forming an easily fusible alloy; the free portions of sulphur and arsenic volatilize, and the sesquioxide of iron and oxide of cobalt dissolve in the borax.

When the scoriæ appear perfectly molten, and free from lead, it is only necessary to submit the alloy for some moments to the outer flame, when the last traces of sulphur and arsenic will be expelled.

The fusion of argentiferous minerals should always be accomplished in the reducing flame, because if the assay be treated with the oxidating flame, exact results cannot be expected: a considerable portion of the lead would oxidize at the outset, dissolve in the borax, and, coming in contact with the carbon, be reduced by it, forming globules with small particles of silver, which are intermingled with the recrements; and even if these reunited with

the main bead, they would soon be replaced by others newly formed, undistinguishable from the argentiferous lead.

The time necessary for fusing a non-previously roasted alloy varies from five to eight minutes, according to its fusibility and the quantity of volatile and argillaceous constituents.

The refrigerated globule must be separated from the scoria in the following manner :-The whole mass should be removed with the forceps, wrapped in paper, and placed upon the steel anvil; by a few gentle strokes of the hammer, the recrementitious particles are perfectly detached.

Treatment of the Workable Lead obtained by the Fusion.

The separation of lead from silver contained in workable lead is effected by oxidation at a red heat, with access of atmospheric air, and is based upon the property of lead to oxidize at such a temperature, while the silver remains unaltered. HARKORT divides this process into two stages, the first termed Oxidation, the second, Cupellation.

The Oxidation.

This operation is a very simple process. A cupel of siered bone ashes is prepared by means of the instrument described at page 29, placed upon the mould, and submitted to a red heat in the oxidating flame, to remove all hygroscopic moisture. By this precaution the experimenter will avoid a loss of workable lead.

The cupel being desiccated, is charged with the workable lead, and smelted in a strong outer flame until the surface of the assay brightens, and oxidation commences. If the workable lead contains large portions of copper or nickel, the fusion requires more time, owing to the nickel separating from the lead at the commencement, and covering its exterior with an infusible layer, which prevents access of atmospheric air, and makes the oxidation impossible, the copper renders the alloy but difficultly fusible. If, therefore, much nickel is present, a small quantity of pure lead, -two to four decigrammes,-should be added to the assay.