assay, purpose of slagging off the copper, &c.); it is relatively greater, as the silver globule is larger, but represents a larger percentage of the silver actually contained in the in proportion as the silver globule obtained diminishes in size. It has, however, been experimentally proved that, in assays of like richness in silver, this loss remains constant when the same temperature has been employed, and similar weights of lead have been oxidised in the operation. In the blowpipe assay this loss is not confined to the ultimate operation of cupellation, but occurs, though in a less degree, in the concentration of the silver-lead, and in the previous scorification of the assay, had such operation preceded the concentration. The total loss in the blowpipe assay is found, however, to be less than in the ordinary muffle assay, since in the latter case the whole of the oxidised lead is directly absorbed by the cupel. In mercantile assays of ore it is not customary to pay attention to the cupellation loss, and the results are usually stated in the weight of silver actually obtained. Where, however, great accuracy is required, especially when the substances are very rich in silver, the cupellation loss is added to the weight of the silver globule obtained, in order to arrive at the true percentage. The amount to be added for this purpose is shown in the annexed table, which is slightly modified from Plattner's. The use of this table is best explained by an example, as the following:-An assay to which there had been added, in all, five times its weight of assay lead, gave a globule of silver equivalent to six per cent. Upon referring to the table, it will be seen that the cupellation loss for this would be 0.07; consequently the true percentage of silver contained in the assay would be 6:07. This table is only extended to whole numbers, but fractional parts can easily be calculated from the same. When the globules of silver are so minute that they cannot be weighed, but must be measured upon the scale, the cupellation loss should not be added, since, as a rule, it would be less than the difference which might arise from Actual percentage of silver found by assay Cupellation loss, or percentage of silver to be added to the actual percentage found by assay in order to show the true percentage of silver contained in same. The entire amount of lead in or added to the assay being the following multiples of the original weight of assay:- 60 50 40 0.11 0.13 30 0.10 0.12 0.18 25 20 0.09 0.10 0.14 15 0.07 0.08 0.10 0.16 0.20 0.26 0.30 0.36 0.52 0.61 0.74 0.15 0.20 0.23 0.28 0.32 0.37 0.13 0.17 0.19 0.23 0.26 0.32 0.11 0.15 0.17 0.20 0.23 0.10 0.14 0.16 0.18 0.21 0.09 0.13 0.15 0.16 0.18 0.27 0.25 0.22 0.08 0.12 0.13 0.14 0.16 0.20 0.02 0.04 0.05 0.07 0.10 0.11 0.12 0.14 0.17 0.01 0.03 0.04 0.06 0.09 0.10 0.11 0.12 0.14 0.02 0.03 0.05 0.07 0.08 0.09 010 011 0.01 0.02 0.04 0.05 0.06 0.07 0.08 0.09 0.01 0.03 0.04 0.04 0.05 0.06 0.07 0.01 0.03 0.03 0.04 0.04 0.05 errors of observation likely to occur when measuring their diameters upon the scale. In the case of beginners, it will be found that the cupellation is usually carried on at too high a temperature, and that thereby a greater loss is occasioned than would be accounted for by the above table. After some trials the necessary experience will be acquired in keeping up the proper temperature at which this operation should be effected. It now becomes necessary to consider in detail the processes requisite for extracting the silver contents (in combination with lead) from the various metallic alloys of silver which are met with in nature or produced in the arts. In considering these, the following classification of the substances will be found convenient : I. METALLIC ALLOYS. A. Capable of direct Cupellation. a. Consisting chiefly of lead or bismuth: silver-lead and b. Consisting chiefly of silver: native silver, bar silver, test B Incapable of direct Cupellation. a. Containing much copper or nickel, with more or less sulphur, arsenic, zinc, &c.; unrefined or black copper, brass, german silver. b. Containing tin: argentiferous tin, bronze, bell metal, c. Containing antimony, tellurium, or zinc. e. Containing much iron: argentiferous steel, bears from A. METALLIC ALLOYS CAPABLE OF DIRECT CUPELLATION. a. Consisting chiefly of Lead or Bismuth.-In determining the silver contained in these alloys, it is only requisite to place a clean piece of the same, weighing about from one to ten grains according to its probable richness in silver, upon a cupel of coarse bone ash, and proceed by concentration and cupellation exactly as has been already described under these heads. Should the substance be not altogether metallic, or not free from adherent slag, earthy matter, or other extraneous matter, it should previously be fused on charcoal with a little borax in the reducing blowpipe flame, and the clean metallic globule then removed from the charcoal, and treated as before. In order to remove the globule from the inherent borax glass, it may be allowed to cool, and then detached; or, after a little practice, it will be found easy, by a quick movement of the charcoal, to cause the globule, still melted, to detach itself completely, and drop on the anvil in the form of a single somewhat flattened globule, without suffering any loss of lead adhering to the charcoal. In the case of argentiferous bismuth alloys the process is carried on in all respects the same as if silver-lead were being treated. As, however, the bismuth globule is very brittle, care must be taken when separating the concentrated globule from the litharge, as, if not carefully done, a loss may easily be sustained from a portion of the globule remaining behind adherent to the litharge. It is better, therefore, to remove the litharge by degrees from the globule with the aid of the forceps. Argentiferous bismuth, free from lead, when cupelled alone, invariably leaves a globule of silver, having a dull frosted surface. If, however, at the end of the operation a small quantity of lead (to a grain) be added, and fused along with it, the silver globule then obtained will be perfectly bright and free from all bismuth. In the case of native bismuthic silver it is advisable to fuse the previously weighed mineral with a little lead and borax glass on charcoal in the reducing flame, so as to free it from any adherent earthy matter, and then proceed by concentration and cupellation, as before described. b. Consisting chiefly of Silver: native silver, bar, test, and precipitated silver, retorted silver amalgam, standard silver, silver coin, and other alloys of silver with gold and copper.These alloys may be at once fused with lead on the cupel itself, and the operation finished as before described. In general, however, it is better to fuse the weighed assay previously with the requisite amount of pure lead and a little borax-glass, say from a quarter to half the weight of assay, in the reducing flame at a low heat on charcoal until the globule commences to rotate. This ensures the having a perfectly clean button of silver-lead, which is then cupelled in the ordinary manner. In most cases the quantity of lead to be added need not exceed that of the weight of the alloy, but when several percentages of copper are present in the assay, as in case of many coins, &c., the lead should be increased to some three, or even five, times the weight of the assay in proportion to the amount of copper actually contained in the substance under examination, and which will be treated of more at length under the head of copper-silver alloys. When no more lead has been added to the assay than ૨ ૨ its own weight, the cupellation may be concluded in one operation by inclining the stand, and so moving the globule on to a clean part of the cupel; but when more copper is present, it is preferable to concentrate first and cupel subsequently, in order thereby to reduce the cupellation loss to its minimum. In the concentration as much copper as possible should be slagged off with the lead, which is effected by inclining the cupel somewhat more than usual, so that its surface may be less covered up with the litharge and exposed as much as possible to oxidation, by which means the litharge, as it forms, is enabled to carry off more of the copper contained in the silver-lead. Should the silver globule after cupellation show indications of still containing copper, as before noticed, when treating of cupellation, a small quantity of lead must be fused along with it, and the cupellation finished as usual. As at the present time no means are known by which silver can be separated from gold by the use of the blowpipe, in all cases of alloys containing gold, this metal remains to the last along with the silver, and the result in such cases always indicates the combined weight of both these metals contained in the alloy under examination. The employment of the humid assay must be resorted to for effecting their separation. c. Containing chiefly Copper: native copper, ingot, wire, or sheet copper, cement copper, copper coins, copper-nickel alloys. Under the most favourable conditions in cupellation, the amount of lead requisite, when converted into litharge, to slag of one part of copper along with it as oxide, amounts to between seventeen and eighteen times its weight. In the blowpipe assay it is usual to add to any cupriferous alloy an amount of pure lead equal to twenty times the amount of copper contained in the alloy, in order to ensure the whole of the copper being separated in the litharge. In the case of nickel the amount of lead required is somewhat less than with copper, but in practice the same amount of lead may be employed. When the copper is quite clean the requisite amount of |