COPPER ASSAYING 943 



products are poured out into the ingot mould, quenched in water, and when cold the 

 slag detached from the button of coarse or impure copper. The character of this will 

 vary according to the impurities present. If any regulus is attached to the upper 

 surface it indicates that the previous calcination has been imperfect, and the assay of 

 the ore must be repeated. The slag should be black, and free from all trace of red 

 colour. If the fusion has been properly made, the slag will not require to be cleaned 

 or to be re-fused with reducing agents ; although it is customary for some assayers to 

 clean all such slags. When raw or calcined ores are fused for coarse-copper the 

 addition of more carbonate of soda and borax are generally necessary. A little lime 

 or oxide of iron may also bo added with ores comparatively free from vein-stuff, to keep 

 the slag free from oxide of copper : nitre and tartar are also used for reduction, instead 

 of the carbonate of soda and tartar. 



Refining. This may be conducted in the crucible which has been used for the pre- 

 vious process. If a new one is employed a little borax should be previously fused in 

 it. A hot fire is. necessary. The crucible is fixed in the fuel so that the process can 

 be easily observed through the space of the fire-brick covers, and when hot the copper 

 button is thrown in. When the surface of the metal appears bright and clean about 

 from 100 to 150 grains of the refining flux are quickly projected from the copper scoop, 

 fig. 535, upon it, and the furnace closed. After the lapse of about 2 minutes the cru- 

 cible is removed and the contents poured out into the mould. The button should be 

 flat and have a pit or depression on the upper surface. The fracture is generally dull, 

 granular, and of a red colour, or finely fibrous or silky, and of a salmon-red colour. 

 The slag varies somewhat in colour ; it should be grey, flesh-colour, pink, or pale red. 

 It is powdered, re-fused with tartar or other reducing agents for about 10 minutes, the 

 product poured out, and carefully examined for any shots of metal it may contain. 

 With some assayers it is customary to submit impure copper buttons to one or more 

 washings previous to refining. In washing, the metal and refining fluxes are pro- 

 jected together into the crucible and the product poured out when fused. 



The following is another Method of conducting the Cornish Process. A portion of the 

 pounded and sifted ore is first burnt on a shovel, and examined as to its supposed 

 richness and the amount of sulphur, arsenic, and other impurities it may contain. A 

 little practice in this operation will enable the operator to judge with considerable 

 accuracy of the quantity of nitre necessary in order to obtain a good regulus. 



Fiisionfor rcguLus. Two. hundred grains of the mixed ore are now weighed out and 

 carefully mixed with a flux consisting of nitre, borax, lime, and fluor-spar, and the 

 fusion for matt or regulus is begun. The quantity of nitre used will of course vary 

 with the amount of sulphur and arsenic present ; but the other ingredients are com- 

 monly employed in the following proportions: Borax, 5 dwts. ; lime, l^ladleful; 

 fluor-spar, 1 ladleful. 1 After being placed in the crucible, the whole is generally 

 covered by a thin stratum of common salt. After remaining in the fire for about a 

 quarter of an hour, the fusion will be found complete, and the contents of the pot may 

 be poured into a suitable iron mould. The button of regulus is now examined, in 

 order to determine whether a suitable proportion of nitre has been used. If the right 

 quantity has been employed, the button, when broken, should present a granular 

 fracture, and yield from ' 8 to 10 for 20 ' of copper, i.e. from 40 to 50 per cent. How- 

 ever rank a sample may be, it should never be mixed with above 9 or 9 dwts. of nitre ; 

 and if the amount of sulphur be small, 3 dwts. are often sufficient. The grey sulphides, 

 the red and black oxides, and carbonates, have sulphur added to them for the purpose 

 of obtaining a regulus. Highly-sulphurised samples, requiring above 9J dwts. of 

 nitre, are sometimes treated in a different way. In this case the ores are first care- 

 fully roasted, and afterwards fused with about 5 dwts. of nitre, 9 dwts. of tartar, and 

 3 dwts. of borax. 



Boasting. The roasting of the regulus thus obtained is performed in a smaller . 

 crucible than that used in the fusion for matt. During the first quarter of an hour, 

 a very low temperature is sufficient. The heat is then increased to full redness, and 

 the assay allowed to remain on the fire for a further period of about 20 minutes. 

 During the first 15 minutes it should be kept constantly stirred with a slender iron 

 rod ; but afterwards, an occasional stirring will be found sufficient When nearly the 

 whole of the sulphur and arsenic has been expelled, the temperature must bo raised 

 nearly to whiteness during a few minutes, and the assay then withdrawn and allowed 

 to cool. 



Fusion for coarse-copper. The fusion for copper is effected in the same crucible in 

 which the roasting has been carried on. The quantity of flux to be used for this 

 purpose varies in accordance with the weight of the button of regulus obtained. A 

 mixture of 2 dwts. of nitre, 7$ dwts. of tartar, and l dwt. of borax, is sufficient for 



* The ladle used for this purpose is three-quarters of nn inch in diameter and half- an-inch in depth. 



