the richest ores and those yielding up to 50 per cent., but is greater in poorer ores. In Wales and Flintshire a yield of 75 to 82 per cent. Pb is obtained from pure galena by placing 10 ounces troy of the ore in a covered iron dish and fusing it in an open forge fire.-Bleiberg in Carinthia: 50 grammes (771.61 grains) of ore, 2 tablespoonfuls of flux (3 parts of argol, 2 saltpetre, 1 borax), a cover of powdered glass (or common salt), smelting for 12 to 15 minutes, etc.-Belgium: 10 grammes (154.32 grains) of galena with 28 grammes (432.10 grains) of sodium carbonate and 5 grammes (77.16 grains) borax, or 10 grammes (154.32 grains) sodium carbonate and 10 grammes (154.32 grains) argol.-Tarnowitz: 50 grammes (771.61 grains) of ore, with black flux, borax, and a covering of salt resting upon a layer of a little black flux. The difference between the separate assays is not more than 2 per cent.—Mechernich: 25 grammes (385.80 grains) of ore with 150 grammes (2314.8 grains) of borax and 100 grammes (1543.23 grains) sodium carbonate and argol in equal parts. slag more borax, for lead matt more soda. For b. Assay with potassium cyanide in clay crucibles.— This can be executed at comparatively low temperatures, and gives a good yield, but is more expensive than the foregoing. Besides, the potassium cyanide is poisonous, and adheres to the porous mass of the crucible which may uncover the lead button and effect its oxidation. The charge, according to Levol, is as follows: 100 parts galena, 100 potassium ferrocyanide, and 50 potassium cyanide with some sodium carbonate; according to Ricketts: 10 grammes (154.32 grains) of ore, 20 to 25 grammes (308.65 to 385.80 grains) of potassium cyanide, and a covering of common salt. The charge is fused for 12 to 15 minutes at a low temperature; the yield is 78.5 to 79.1 per cent. of lead. 2. Galena with more earths. a. Assay with black flux (potassium carbonate and flour) and metallic iron, in clay crucibles.-When the ore contains large quantities of earth, more slag is formed. This, if the contents of the crucible were to be poured out, would retain considerable lead, which will settle if the charge is allowed to cool off in the crucible. The loss of lead is from 2 to 3 per cent. Deep crucibles (fig. 39, p. 66) are used for this purpose, and the charges fused in a muffle or wind furnace. The work can be done more conveniently in the latter, and fuel will also be saved. Should small quantities of metallic sulphides be present, it is well to roast the ore somewhat in a covered crucible to volatilize the arsenical sulphides, the sulphur from the iron pyrites, etc. Charge: 5 grammes (77.16 grains) of galena are placed on the bottom of the crucible, upon this is put a piece of iron wire 4 to 5 millimeters (0.157 to 0.196 inch) thick, and up to 9 millimeters (0.354 inch) long (it should be longer or shorter according to the percentage of lead, that is to say, about 25 to 30 per cent. of the weight of the ore). Upon this are placed 15 grammes (231.48 grains) of black flux (or potassium carbonate with 15 to 20 per cent. of flour) and, in case of basic gangues, 2 to 3 grammes (30.86 to 46.29 grains) of borax. Upon this comes a covering of common salt 5 millimeters (0.197 inch) thick, and on top of all a piece of charcoal the size of a hazel-nut, for maintaining a reducing atmosphere. The contents of the crucible are slowly heated in the muffle furnace until the yellow flame caused by the carbonization of the flour is no longer visible. The heat is then raised, and tongues of bluish flames arising from the carbonic oxide will make their appearance. The contents of the crucible should not froth too strongly, and for this reason the firing must be done very carefully, especially when low crucibles are used. When the "flaming" and frothing have ceased, the heat is still kept up forto of an hour to allow the sulpho-salt (p. 86) to become decomposed by the metallic iron. 25 to 30 minutes are required for fusing the charge. The sample, fuming strongly from the vapors of the common salt, is then taken out, allowed to cool off, and freed from slag. By hammering the lead flat, the iron adhering to it will fly off. The lead button, which is covered with iron sulphide, is then brushed and weighed. The success of the assay is indicated by the iron still adhering to the lead without this being wrapped around it (to prevent this, the iron wire should not be too fine), by thoroughly fused slag and a malleable lead button. If brittle, it contains sulphur. The various assays must agree within 1 to 3 per cent. according to the richness of the ore. Freiberg: 3.75 grammes (57.87 grains) of ore, 0.92 to 1.13 grammes (14.2 to 17.44 grains) of iron wire; 7.5 to 9.4 grammes (115.7 to 145 grains) of black flux or potassium carbonate with flour, 1.13 to 1.5 grammes (17.44 to 23.15 grains) of borax, and for basic gangue 2.25 to 2.63 grammes (34.73 to 40.6 grains) of glass, and a covering of common salt, 5 millimeters (0.196 inch) thick. The charge is heated fromto 1 hour in the wind-furnace.-Pribram: 0.5 gramme (7.71 grains) of crude argol is placed in the bottom of the crucible, upon this iron wire, then 5 grammes (77.16 grains) of galena, and 12 grammes (185.1 grains) of black flux, and finally a covering of common salt. The charge is heated from 20 to 25 minutes in a gently glowing windfurnace until the fusing mass subsides. The fire is then urged on, when the assay will emit gas (boil) vigorously, and, when this is the case, the firing is continued for 5 minutes longer. A difference of 2 per cent. is allowed in the assay of ores with 0 to 50 per cent. of Pb, and 3 per cent. in those with over 50 per cent.—England:1 The same quantities of ore and flux are used as for assays in the iron pot (p. 87). The ore is placed in a Hessian crucible together with to of the flux, and a strip of wrought iron in the shape of a horse-shoe is pushed into the mass. The crucible is gradually heated, requiring from 20 to 25 minutes, and during this time the iron is moved about several times. When the flux is thin fluid the crucible is taken from the furnace, the iron, which should be free from globules of lead, is removed, and the crucible allowed to cool. The contents is then poured out, and the lead button is freed from slag. If the heat has not been strong enough, the lead button will be hard, and will have a lustre like 1 B. u. h. Ztg. 1871, p. 62. galena, and the slag will also be covered with a lustrous film. The yield of lead from pure galena is from 82 to 83 per cent. of Pb.-New York: 10 grammes (154.32 grains) of ore, 25 grammes (385.80 grains) of black flux, three loops of iron wire, which are taken out after the fusion is complete, and a covering of common salt. The yield from pure galena is 78.4 to 78.6 per cent., with a difference of 1 to 2 per cent. in the various assays.-Upper Harz: The assay was formerly conducted in the same manner as in Freiberg, but now iron pots are used. b. Upper Harz, assay with potassium carbonate.-A muffle-furnace is required for this method of assaying. Low crucibles (Fig. 39) may be used, as the charge contains no carbon, and several crucibles can be placed in the muffle at one time. The result of this assay is not as accurate, the yield being somewhat less than with the methods described above, as the success of the operation depends on the proper "cooling of the assay," for which there is no guide but experience. This method is therefore chiefly available for uniform ores only, the approximate yield of which is known. It has been almost abandoned at the present time. Charge: 12.5 to 15 grammes (192.90 to 231.48 grains) of potassium carbonate are placed in a small crucible (Fig. 39, p. 66). To this is added 5 grammes (77.16 grains) of galena, and both are thoroughly stirred together with the mixing spatula. In case basic earths are present, 1 assay spoonful of borax is placed upon the mixture, and upon this a covering of common salt 5 millimeters (0.196 inch) thick. The charge is then placed in the thoroughly heated muffle-furnace, where it remains, with the mouth of the muffle closed, until it has come into perfect fusion (that is, when no more deposits are perceptible on the edges of the crucible). To decompose the sulpho-salt by oxidation, the mouth of the muffle is then opened for about 10 to 15 minutes, until the crucible ap pears dark and the vapors above it have greatly diminished or entirely disappeared (this is called cooling the assay). Thereupon the furnace is brought back to its first temperature, completely closing the muffle, in order to decompose the still remaining sulphurized lead by the sulphate which has been formed: The crucible is then taken out and allowed to cool off, and the lead buttons are freed from adhering slag. If the assay has been successful, the slag is completely fused, and the lead button. has a pure lead color, but not much metallic lustre, as, if this is the case, the heat has been too strong.-For ore containing antimony: 10 grammes (154.32 grains) of ore, 35 grammes (540.13 grains) of potassium carbonate, 1 gramme (15.43 grains) of saltpetre, and a covering of common salt. 30 minutes are required for fusing, 10 minutes for cooling, and 10 minutes for the final heating of the assay. 3. Galena containing large quantities of earths.-The English method (p. 87) is employed with a strip of sheetiron in the form of a horse-shoe, but stronger fluxes (caustic alkalies) are used, which, to be sure, attack the crucibles more energetically, and larger charges, as for instance: 100 grammes (1543.23 grains) of assay sample, 100 to 150 grammes (1543.23 to 2314.8 grains) of caustic soda, 150 to 250 grammes (2314.8 to 3858 grains) of potassium carbonate or sodium carbonate, strip of iron in the form of a horse-shoe 25 millimeters (0.098 inch) wide, and 4 millimeters (0.157 inch) thick. From 1 to 1 hours are required for perfect fusion, and until the iron is free from lead globules. B. Lead monosulphide with foreign metallic sulphides (galena with zinc blende, iron pyrites, etc.; lead matt, etc.). 1. Roasting and reducing assay.-The result of this assay is inaccurate, as the lead oxide is liable to slag off |