944 COPPER ASSAYING 



the reduction of a calcined rcgulus that, previous to roasting, weighed from 45 to 50 

 grains. In the case of a button weighing from 90 to 100 grains, 3i dwts. of nitre, 

 9 dwts. of tartar, and 2 dwts. of borax, should be employed. These quantities are, 

 however, seldom weighed, since a little practice renders it easy to guess, with a suffi- 

 cient degree of accuracy, the necessary amounts. 



Refining. The prill of copper thus obtained is seldom fine, and consequently re- 

 quires purification. A crucible is heated to redness in the furnace, the metallic button 

 is taken from the mould and thrown into it, and some refining flux and salt are placed 

 in a scoop for immediate use. 1 In a few minutes the fusion of the prill is effected. 

 The crucible is now taken from the fire by a pair of tongs, the contents of the scoop 

 introduced, and a gentle agitation given to it ; an appearance similar to the bright- 

 ening of silver on the cupel now takes place, and the crucible is returned to tho fire 

 for about four minutes. The crucible is now removed, and its contents rapidly poured 

 into a mould. The button thus obtained will consist of refined copper, and present a 

 slight depression on its upper surface. The slags from the reducing and refining 

 operations are subsequently fused with a couple of spoonfuls of crude tartar, and the 

 prill thus obtained weighed with the larger button. 



2. German Method. This method is used in Germany and other parts of Europe, 

 for the estimation of copper in ores and other substances. It consists essentially of tho 

 following processes : 1. Eoasting or calcination; 2. Eeduction or fusion for black 

 copper; 3. Refining. 



Furnace, $c. A muffle furnace is employed. The form and dimensions of a muffle 

 furnace vary somewhat ; the construction depending on the nature of the fuel employed 

 and other circumstances. If bituminous coal is used, the muffle is heated by tho flame 

 of the fuel, and the fire-grate is placed at some distance below. When anthracite coal 

 or charcoal is employed the muffle is surrounded with hot fuel. Scarifiers or roasting 

 dishes ; flat shallow vessels made of fire-clay about 2g inches diameter and 1 inch 

 deep inside measure. Crucibles ; thin oval shaped vessels of fire-clay, provided with a 

 flat foot about 4 inches high and If inch internal diameter at the widest part. Tongs, 

 scoop, pestle and mortar, and other implements are required. For a description of a 

 muffle furnace, see SILVER. 



Weights. Special assay weights are used in Germany. 1. Assay centner = 100 

 assay pounds; 1 assay pound = 100 assay part pounds. The assay centner weighs 

 3 75 grammes, or about 58 grains. 50 grains of the substance may be taken to operate 

 on when grain weights are used. 



Fluxes, $c. Black flux, the product obtained by deflagrating 1 part of nitre and 2 

 of tartar, or a mixture of alkaline carbonate and charcoal, or substitute for them borax, 

 glass, salt, graphite, charcoal-powder, lead, arsenic, antimony, iron pyrites. For the 

 purpose of assay by this method the ores and other substances may be divided into : 1, 

 Oxidized ores, &c. which require reduction and refining ; 2. Sulphurous ores, &c. which 

 require calcination, reduction, and refining ; 3. Ores, &c. poor in copper, which require 

 fusion with iron pyrites to obtain a regulus : the regulus is afterwards treated accord- 

 ing to 2 ; 4. Varieties of impure copper, which require refining with lead. 



Process : Eoasting. 50 grains of the ore mixed with about \ of its weight of graphite 

 powder or other substitute and spread over the bottom of a scorifier or roasting dish 

 previously coated inside with red oxide of iron. The scorifier is now placed in a 

 muffle at a low red heat, and the calcination continued until the graphite ceases to glow 

 and the odour of sulphurous and other gases is no longer perceptible. This is then 

 removed, and the product powdered, remixed with about 5 per cent, or more of charcoal- 

 powder, and recalcined. This operation is repeated a third time if necessary. The 

 calcination is completed in about 30 minutes. Carbonate of ammonia is sometimes 

 added to complete the calcination. 



Fusion for Black Copper. The powdered calcined product is transferred to the oval- 

 shaped crucible, and covered with about twice its weight of black flux, and borax or 

 glass or both added as required. The whole is covered with a layer of salt, and over 

 this is placed a piece of charcoal about an inch square ; a cover is then inserted. Lead, 

 arsenic, or antimony or their oxides are also added when necessary as collecting agents 

 to alloy with the copper and render it more fusible. The fusion is conducted in a 

 muffle ; the temperature is gradually increased from a red heat and the operation 

 completed in from 30 to 40 minutes. The crucible is removed, and when cold, broken 

 open. The button of copper should bo perfectly fused and free from regulus. The 

 slag should be well fused, glassy, and free from a red colour. 



Refining. This is conducted in a muffle upon a flat shallow pieco of broken crucible 

 about from 1 to H inch square. This is placed between hot charcoal, as, a high tern- 



1 The refining flux consists of two parts of nitre and one of white tartar fused together, and sub- 

 sequently pounded. 



