Gold can be separated in the dry way, like silver, from substances in combination.

As it is not susceptible of oxidation, even when treated with borax or lead in the outer flame, and sustains no loss in the cupellation, its per centage in ores, minerals, furnace products, et cetera, may be ascertained with the greatest exactness. The examination for gold, however, is more difficult than for silver, as, in most instances, gold, submitted to Blowpipe analysis, contains a quantity of the latter metal, which in native gold varies from 2 to 35 per cent.

From examinations of silver ores dressed in the Freyberg works for gold, the following results were obtained :—

Videlicet. That all sulphides of iron holding from 0.0142 per cent. to 0-456 per cent. of silver, contain gold. This metal forms an ingredient also of the furnace products which are produced in the smelting of auriferous silver ores.

The various auriferous substances are brought, according to their nature and composition, under several heads; thus :—

TA. Gold Ores, Auriferous Silver Ores, and Furnace Products containing Gold and Silver.

b. Gold and Silver, alloyed with other metals.

c. Gold and Mercury.

Examination of Gold Ores, Auriferous Silver Ores, and
Furnace Products containing Gold and Silver.

Under this class are ranged

1. Native Tellurium, containing, according to KLAPROTH 0·25 per cent. gold, but no silver.

2. All ores and minerals, containing silver, and also gold; as Graphic Tellurium,-Graphic Gold,—the composition of which is 60 tellurium, 30 gold, and 10 silver;-according to BERZELIUS, it contains 52.0 tellurium, 240 gold, 11.3 silver, 1-5 lead. Yellow Tellurium,-Weiss-silvanerz, containing, according to KLAPROTH, 44.75 tellurium, 26.75 gold, 19.50 lead, 8.50 silver, and 0·50 sulphur; Black Tellurium, composed of 32-2 tellurium, 54·0 lead, 90 gold, 0.5 silver, 13 copper, and 30 sulphur; Noble Molybdena Glance, was found to contain 49 gold, and about 0.3 silver.

3. All argentiferous sulphides of Iron and Copper. 4. Roh- and Blei-stein.

5. The auriferous dross of gold- and silversmiths.

Of Gold ores, containing little or no silver, a quantity sufficient for one examination is prepared, and treated in the same manner as an assay of silver. After cupellation, the color of the globule must be observed, for if only 2 per cent. of silver were present, the gold would acquire a brass color. If the gold be pure, which is known from the color, its weight may be determined either upon the balance or the scale. When its color is very light, it it must be submitted to a new treatment, which will be hereafter described.

Of substances containing more silver than gold, a portion of 10 to 15 decigrammes must be reduced to powder, dressed and treated as in an examination for silver. From the quantity of silver yielded, the number of assays necessary for obtaining a sufficient quantity of gold, to make a quantitative determination, is calculated. Should the substance contain not more than 0.114 per cent. of silver, a considerable quantity of it ought to be pulverized, and at least 2:5 grammes taken; on the contrary, if the per centage be larger, exempli gratia, 0·29 per cent., 10 to 15 decigrammes are sufficient for an examination. The dressing of the assay with lead and borax is effected in exactly the same manner as an argentiferous one, but when copper is present, the proportion of lead must be augmented. The fusion and cupellation can also be achieved in a similar way to the assaying of a silver alloy.

Sulphides or minerals containing large quantities of sulphur, and little silver, are analyzed in the following way:-24 to 36 decigrammes of the pulverized substance are divided into parcels of three decigrammes each, placed in a clay basin, the inside of which is covered with a coating of reddle, and roasted without addition of charcoal, like a copper assay.

When nearly all the sulphurous vapor is eliminated, the assay is to be repowdered, and heated until no appreciable quantity of sulphur remains. This being accomplished, the residuum must be placed in a porcelain basin, over a lamp, and treated with a sufficient quantity of hydrochloric acid to dissolve out the formed oxide of iron or copper. The metallic oxides and the silver being dissolved, the gold, with some extraneous matters, will remain The solution is then to be evaporated to dryness, and treated with boiling water. The soluble chlorides dissolve, and are to be separated from the chloride of silver, et cetera, by filtration and edulcoration. The filter holding the insoluble ingredients is to be dried, and after desiccation opened, and dressed cautiously with five decigrammes of lead and one decigramme of borax. The dressed assay must now be placed in a charcoal cavity, submitted to a feeble oxidating flame, in order to carbonize and consume the filter, and then treated with a strong reducing flame. In this operation the chloride of silver is decomposed, its base alloying with the lead and gold, the earthy constituents being dissolved in the borax. The metallic alloy is oxidized and cupelled in the ordinary way, and the auriferous silver globule obtained treated according to the described method for the separation of gold from silver. It sometimes happens that sulphides containing less than 4 loths, 0.114 per cent. of silver, are to be analyzed.—1 loth 14.58808 grammes 239-68 English grains. In this case, 36 decigrammes are not sufficient, therefore, according to the per centage of the noble metal, the following proportions must be taken, videlicet:-Of a substance containing,

=

3 loths 00939 per cent. of silver, 48 decigrammes.

=

As the weighing of a quantity of nearly 290 decigrammes in portions of three decigrammes each, would be very troublesome, it is sufficient to weigh upon an ordinary balance, according to the apothecaries' weight, of an ore containing,—

For the same reason, as it would be exceedingly inconvenient to roast a substance in parcels of three decigrammes each, the following expert method may be undertaken :—

Upon an iron foil, bent into a basin shape, place the whole assay, besmeared several times with clay water, and well dried; and submit it to a strong red heat, continually stirring with a platinum spatula until no more sulphurous acid vapors are evolved, then triturate the residuum in a mortar, and subject the powder to a second roasting.

The assay, after these operations, must be introduced into a porcelain basin, placed over a spirit-lamp, treated with hydrochloric acid, evaporated to dryness, and then mixed with a quantity of water to dissolve out the soluble chlorides, the menstruum filtered, what remains on the filter edulcorated, desiccated, and, if it exceeds one decigramme, weighed in parcels of one decigramme each.

Each decigramme of this residue is to be dressed with

Lead, 5 decigrammes ;

Borax, 1 decigramme;

fused like an argentiferous assay, and cupelled as already stated. The treatment of the auriferous globule will de described in the subsequent paragraphs.

a.

¶ B. Metallic Compounds.

EXAMINATION OF SUCH AS CONTAIN SILVER AND GOLD ONLY.

To these belong native gold, alloys of gold and silver, and the argentiferous gold, or auriferous silver, obtained from the assayings of auriferous minerals and ores.

As, up to the present time, no process is known for separating gold from silver in the dry way, the moist way, termed in this instance Quartation, or Refining of Gold and Silver, must be employed.

For effecting the separation, the proportion of the gold to the silver should not exceed 1 to 3, as, if more gold be present, the solution will be performed either imperfectly, or not at all. When the gold is more than the above proportion, it so protects the silver, that even when hot fuming nitric acid is poured over the alloy, a very slight action only ensues. It is therefore indispensable to make a preparatory assay for determining the composition of the alloy, and if too small a portion of silver be present, add a quantity sufficient for producing the given standard.

Gold containing even no more than 2 per cent. of silver, is, as has been previously stated, of a brass color; if 30 per cent. of silver are present, it appears lightly brass colored, but when the quantity of silver amounts to 60 per cent., a yellow color is no longer perceptible. Therefore, from the intensity of the tinge in an auriferous alloy, conclusions as to its composition, and the necessary quantity of silver, can be drawn.

When native gold of a brass color is to be assayed, it is generally supposed that the per centage of silver associated with it is not high; in this case 20 to 30 milligrammes of the alloy are weighed, fused with 3 x 20 = 60, to 3 x 30 = 90 milligrammes of pure silver,-reduced from the chloride of silver,— and a small quantity of borax, in the reducing flame. Of a light colored auriferous body, 50 milligrammes are weighed for examination, and alloyed in the same manner with 50 × 2 100