198 Mr. J. Napier on Copper Smelting. 



Mix intimately 400 grains of the ore with twice its weight of 

 the above flux, and fuse in a crucible for ten minutes ; if the ore 

 is very siliceous, a little more of the flux is used. When the 

 crucible is cold, break it, and the mat or regulus is found at the 

 bottom ; the slag is a glassy homogeneous mass. The regulus 

 is calcined and proceeded with as before described. 



Besides these methods of assaying by the dry way, or fire, 

 there are various methods practised by acids, or what is termed 

 the wet way. The first is the precipitation of the copper by 

 caustic potash : take 25 grains of the ore, and digest or boil for an 

 hour in a mixture of two parts nitric acid and one hydrochloric 

 slightly diluted with water ; to this add ammonia till the whole 

 smells strongly of that alkali, then pour the whole upon a paper 

 filter, and when the liquid has passed through, wash the contents 

 of the filter by pouring over it water containing a little ammonia : 

 this washing is continued until the water passing through is 

 colourless. The whole liquid obtained is put into a flask or beaker 

 and boiled ; when boiling, add some caustic potash or soda, and 

 continue the boiling until the blue colour disappears, and there 

 remains no smell of ammonia ; the copper then forms a black 

 precipitate. This solution with precipitate is now put upon a 

 paper filter, and the precipitate washed with hot water until the 

 water passing through the filter ceases to turn red litmus paper 

 blue ; the filter is then dried, and the precipitate scraped ofi" the 

 filter into a porcelain crucible ; the paper is burned on the cover 

 of the crucible exposed to the air, and the ashes laid on the top 

 of the precipitate ; the crucible with contents is then brought to 

 a dull red, and afterwards weighed. The substance thus ob- 

 tained is oxide of copper, every 40 parts of which are equal to 33 

 of copper ; the result is thus calculated by the common rule of 

 proportion, and the quantity of copper in the 25 grains ascer- 

 tained. This method is tedious, and requires great care to obtain 

 accurate results ; and the results are always higher than can be 

 obtained by furnace operations. 



Another method often practised is by digesting in acids as 

 stated above, and, after filtering the blue solution obtained by am- 

 monia, evaporating to dryness, rcdissolving the dry residue in a 

 little hydrochloric acid, and then diluting with water and adding 

 a piece of iron or zinc, when the copper precipitates in a metallic 

 state upon either of these metals. When the whole is precipi- 

 tated, the zinc or iron is washed and the precipitate collected 

 upon a weighed filter, washed, dried and weighed : the first 

 washing-water sliould have a little sulphuric acid added to it, 

 and the washing afterwards continued till no trace of acid is left. 

 With care, very accurate results may be obtained by this method, 

 but it is tedious. 



Another and very simple plan is by colour. The operator 



