042 COPPER ASSAYING 



of lead ; tartar or araol ; lime, dry ; fluor-spar, free from copper or lead ; nitre ; charcoal- 

 powder ; carbonate of soda, dried ; salt ; sulphur ; iron pyrites, free from copper, or sul- 

 phide of iron. Refining flux the product obtained by deflagrating a mixture of from 

 2 to 2^ parts by measure of tartar, 3 of nitre, and 1 of salt. (See ASSAY). The fluxes 

 are usually measured, but the better plan is to weigh them, especially until experience 

 is gained. 



For purposes of assay by this method, the ores, &c. may be conveniently divided 

 into : 1. Ores containing over 30 per cent, of copper : a, oxides, carbonates, silicates, &c., 

 which require fusion for coarse-copper and refining ; b, various sulphides comparatively 

 pure or containing arsenic or antimony, which require calcining ' sweet,' fusion for 

 coarse-copper and refining ; 2. ores containing less than about 30 per cent, of copper, 

 which require the fusion for regulus ; a, yellow copper ores, with or without iron pyrites, 

 blende, galena, &c., which require partial calcination or warming, or the addition of 

 nitre, or both, to remove the excess of sulphur ; b, grey copper ores, poor oxides, car- 

 bonates, silicates, and poor antimonial and arsenical copper ores, which have been 

 roasted sweet, which require the addition of sulphur or of sulphur and iron or iron 

 pyrites to yield a proper regulus ; c, purple copper ore, mixed oxides and sulphides, 

 which yield a proper regulus by direct fusion. 



To assist in forming an opinion as to the character of the ore, nature of the 

 associated vein-stuff, and approximate per-centage of copper, a portion of tho sample 

 may be vanned or washed, calcined, or tested by the mouth blowpipe, or by a pre- 

 liminary fusion for regulus. This will enable the assayer to determine beforehand 

 how the ore is to be treated. 



For the formation of a proper regulus, containing about 50 per cent, of copper, tho 

 following data may serve as a guide : 



100 grains of copper pyrites will require about 75 grains of nitre to yield a good 

 regulus. 



100 grains of iron pyrites will require about 180 grains of nitre to oxide it, and 

 cause it to pass into the slag. 



100 grains of grey copper ore or disulphide of copper will require about 60 grains 

 of sulphide of iron, about 82 grains of iron pyrites, or about 55 grains of haematite and 

 excess of sulphur to yield a proper regulus. 



The quantity of ore operated on will vary from 100 to 400 grains according to 

 amount of copper present. 



Process: Fusion for regulus. The largest size Cornish crucible is employed. The 

 raw or calcined ore is mixed with the appropriate fluxes ; about from 1 50 to 200 grains 

 each of lime, glass, borax, and fluor-spar, will form a suitable mixture for many ores. 

 The nitre, or iron pyrites or sulphur, is added according to circumstances. The crucible 

 and its contents are submitted to a high temperature for about 15 minutes, and when 

 tranquil the fused products are poured out into the iron mould, fig. 534. When tho 

 slag has set, the whole is dipped into water, removed, and when cold the regulus 

 afterwards carefully detached from the slag. A good regulus is reddish-brown in 

 colour, very tender, and easily reduced to powder ; it should contain about 50 per cent, 

 of copper, but may vary from 40 to 60 per cent. If the regulus is too coarse it resembles 

 iron pyrites or copper pyrites in appearance, and contains too much iron and sulphur, 

 and the ore requires more calcining, or the addition of more nitre during fusion. If the 

 regulus is too fine, it is black in colour, hard, and the external surface is very smooth 

 and bright : it indicates that tho ore requires more sulphur or iron pyrites, or a sub- 

 stitute for them in the fusion. The slag should bo uniform in colour, but it may be 

 white, green, or black, according to the nature of the ore. It should bo free from all 

 trace of red colour, which would indicate the presence of copper. The slag should be 

 examined for any shots of regulus. 



Roasting or calcination. The smallest or intermediate-sized crucible is used according 

 to the weight of the ore or regulus. A dull fire is required to commence with. Tho 

 finely-powdered substance is transferred to the crucible ; this is placed on the top of 

 the fuel, mouth frontwards, and in an inclined position to facilitate oxidation. The 

 substance is constantly stirred with the calcining rod, fig. 537, especially at the first 

 part of tho operation, and the heat is afterwards increased to a bright red. The cal- 

 cination should be completed in about 30 minutes. If any sign of clotting or softening 

 of the particles occur, the crucible must be removed, and, if necessary, the product 

 repowdered, mixed with some anthracite-powder or coke-dust, and recalcined. Calci- 

 nations may also be made in scorifiers or roasting dishes in a muffle furnace. 



Fusion for coarse-copper. This is effected in the crucible used for calcination. The 

 calcined ore or regulus is mixed with about from 50 to 150 grains of carbonate of soda, 

 from 50 to 150 grains of tartar, and from 20 to 30 grains of borax, and exposed to a 

 high temperature for about 16 minutes. The temperature should be sufficient to reduce 

 the oxide of copper and molt the metal, and leave the oxide of iron in the slag. The 



