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acid, iu the form of sulphate of ammonia, leaving oxide of co^^per and 

 oxide of iron, the former of which is easily reduced to a metalUc state. 

 The roasted ore is then mixed with 900 grains of carbonate of soda, 

 20 grains of carbon or lamp-black, and 20 grains of lime, introduced 

 into the same crucible and covered with 20 grains of borax, and smelted 

 in the assay furnace until the whole mass becomes perfectly liquid, 

 when it may be withdrawn from the fire and allowed to cool ; the 

 crucible is then broken, and a button of copper will be found at the 

 bottom. The small piece of metal obtained by this fusion must be 

 beaten under the hammer, and if it is perfectly malleable, without 

 cracking at the edges, the button may be considered as fine or pure 

 copper ; if not, it has to be refined by repeatedly fusing it with about 

 20 grains of a mixture of carbonate of soda, nitre, and common salt, 

 until the metal becomes perfectly malleable. 



All kinds of copper ores cannot be assayed by this method. The mode 

 of treatment varies according to the composition of the ore, and as 

 copper pyrites is the ore which comes chiefly under our notice, I have 

 thought it sufficient to describe the mode of assaying this mineral. 

 The dry assay yields the amount of copper which the smelter obtains 

 on the large scale ; but if he wish to know the exact quantity of copper 

 that the ore contains, we must have recourse to the humid assay. 

 The following methods are those generally used for this purpose : — 



Copper is generally determined as an oxide by precipitation with a 

 fixed caustic alkali. For this pui*pose the ore is dissolved in a mixture 

 of nitric and hydrochloric acids until nothing but a siliceous matter is 

 left ; if any other metals but iron are present, they must be separated 

 according to the routine of chymical analysis ; if the latter metal, 

 however, is the only one present, it is only necessary to dilute the 

 solution aird add ammonia in excess, which precipitates the iron, the 

 copper being held in the solution, which, as we have already observed, 

 has a beautiful blue colour. The iron is separated by filtration and 

 the filtrate boiled ; as soon as the liquor has reached the boiling 

 point, a solution of caustic potash, or caustic soda, is added to it, the 

 blue colour disappears, and the whole of the copper will be precipitated 

 in the form of an oxide, if the experiment be conducted successfully. 

 The precipitate is thrown upon a filter, carefully washed, dried, and 

 ignited in a platinum crucible ; from the amount of oxide of copper 

 obtained, the amount of metallic copper is calculated, forty gi'ains of 

 oxide being equivalent to thirty-two grains of copper. If the ore be 

 rich, fifty grains will be found sufficient to analyze ; if it be poor, it 

 will be found necessary to use one or two hundred grains. There are 

 several other methods of determining the amount of copper in an ore. 



