142 EECENT COPPER-EXTRACTINa PROCESSES. 



reduced to a metallic state, subsequently to wHcli it has to be 

 run in a furnace and refined. It would be premature to offer 

 here an opinion of the merits of this invention, and the mention 

 of it is made here because the subject would be incomplete if it 

 were ignored. Several attempts have of late years been made in 

 Europe to reduce iron by the direct application of hydrogen, with 

 more or less success. 



The AMMOifiA Process 



is the invention of Dr. Thomas Clarke and Mr. E. Smith, F.C.S., 

 and specially intended for ores containing silver. If sulphides, 

 they are roasted, to convert into oxides ; usually, even after care- 

 ful roasting, some of the copper and silver will remain in the 

 form of sulphates, though the iron be completely oxidized ; the 

 rest will consist of oxides, and possibly a small quantity of metal- 

 lic copper. The charge is then treated with calcic chloride, 

 which removes all the sulphuric acid, forming calcic sulphate, 

 while the copper and silver are converted into chlorides. At this 

 stage ammonia is added, which forms chloride of ammonium ; and 

 this, with the free ammonia, dissolves the copper and silver, 

 whether they exist as chlorides, oxides, subsalts, or finely divided 

 metallic particles. The ammoniacal solution is then passed into 

 a platinum tank, where the silver is deposited at the expense of 

 the copper sheets in the tank, such copper being taken up in 

 solution and recovered in a subsequent process. When all the 

 silver is deposited, the solution is passed into a tank, a little 

 caustic alkali added, and superheated steam admitted. The cop- 

 per is precipitated as oxide, the ammonia being expelled, and 

 recovered in condensers for subsequent use in fresh operations. 

 At first sight it might appear that the cost of the ammonia would 

 be considerable, but it is found that the loss is very small, nearly 

 the whole being recovered without any additional expense ; it is 

 said to be in no way an objection to the process. The wear and 

 tear of the platinum is infinitesimal, and the copper plates are 

 easily renewed, while the copper dissolved is recovered. The 

 copper plates require renewal only once in three months if fifty 

 tons per day be worked. It is claimed that a very small amount 

 will cover the cost of plant, while the material consumed is less 

 costly than with any chlorinization process. In England calcic 

 chloride is very cheap, being a waste product, but how far it 

 would be available here remains to be ascertained. It would 

 appear, however, that with oxides and carbonates the calcic 

 chloride will not be required ; and the same remark applies to 

 ores ihorouglily calcined, and containing neither sulphides nor 

 sulphates. It is necessary that the ore be ground very fine, and 

 that as much as possible of the sparry gangue shall be eliminated 

 before treatment. Of course sodic chloride may be substituted 



