to Percy, at the following rate: 1.80 to 7.90 per cent. when the ore contains from 10 to 90 per cent. of calcium carbonate, and 1.18 to 35 per cent. when 10 to 90 per cent. of silicic acid is present. The sample is less frequently fused without any fluxes (Flintshire) than with alkaline fluxes. An addition of carbon (black flux, flour, argol) checks the oxidation of the lead, promotes the reduction of the lead carbonate and lead sulphate which may be present, and prevents the oxidation of the iron sulphide. The latter (oxide of iron) vigorously attacks the walls of the pot and retains particles of lead when the contents of the pot are poured out. Fluor-spar is a good flux for heavy spar. Silver and gold pass entirely into the lead, but only traces of zinc and iron. Copper divides itself between lead and slag. A large part of the antimony passes into the lead, and while a part of the arsenic volatilizes, very little of it passes into the lead and the largest part forms spiess with iron.

50 grammes (771.61 grains) of ore are placed in an iron pot previously heated to dark redness, in a coke fire in the wind furnace, or in a gas furnace. From 50 to 100 grammes (771.61 to 1543.23 grains) of black flux or potassium carbonate with 15 to 20 per cent. of flour are added, then 2 to 3 grammes (30.86 to 46.29 grains) of borax, and finally a covering of common salt 5 millimeters (0.197 inch) thick. The charged crucible is then placed between the darkly glowing coal in the furnace. The latter is closed, and the temperature gradually raised in about five minutes to complete redness, and this is kept up until the contents of the crucible are in quiet fusion without foaming (three to five minutes). The granules of lead floating on the top should be submerged

B. u. h. Ztg. 1871, p. 61.

by means of an iron spatula or wooden rod. The furnace is then closed for a few minutes, after which the pot is taken out and allowed to cool off somewhat. Its contents are poured into a mould, which should have been previously coated with graphite and heated. If the contents are poured out while too hot, a film of lead may remain adhering to the iron, and, if too cold, the lead will partly spread over the slag. The mould, after having been al lowed to cool off, is turned over, and the hard, black slag is quickly broken off from the lead button to prevent it from becoming moist, as it would then not separate quite as well. The lead button is then washed with hot water or diluted sulphuric acid, dried, and weighed. The slag is again smelted with some potassium carbonate and flour or black flux for about 10 to 12 minutes, and then poured The time required for the fusion, counted from placing the ore into the pot to the first pouring out, is from 10 to 15 minutes. The iron pots will bear from 40 to 50 operations. In many works lead matt free from copper, poorer ores, and slag are assayed according to this

out.

method.

England (Flintshire): 500 grains (32.4 grammes) of rich galena, 500 grains sodium carbonate, and 50 grains argol; for poorer ores: 350 grains of sodium carbonate, 150 grains borax, and 50 grains argol. The ore is mixed in a mixing scoop with a long spout (Fig. 6a, p. 32), with three-fourths to four-fifths of the quantity of the flux. The mixture is pushed to the front of the scoop, next to this the remainder of the flux is placed, and behind this the borax. The whole is then carefully poured into the dark glowing pot and subjected to the fusing operation mentioned above. In pouring out the contents the slag is kept back in the pot by means of a wooden rod, and is again fused with 20 to 30 grains of sodium carbonate and 5 to 10 grains of argol. The yield of lead from pure galena is generally from 84.25 to 85.25 per The difference in the results of the assay is nearly the same for

cent.

1 B. u. h. Ztg. 1862, p. 242; 1871, p. 61.

:

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 for to 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 from 3 to 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: 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.