58 president's address — section b. 



then to remove them from the hqiiid by precipitation. In 

 this way we can separate out gold, copper, zinc, silver, and 

 lead. 



In the case of chlorination the sources of the active 

 chlorine are : — 



1. The decomposition of bleaching powder either by 



acids or acid sodium sulphate. 



2. The direct use of the chlorine liberated by electrolysis. 



3. Roasting the ore with salt. 



The first of these methods is open to serious objection 

 owing to the wasteful loss of chlorine, and the difficulty of 

 transporting oil of vitriol over rough country. Both of the 

 other methods have much to recommend them in a country 

 like Australia. 



Amongst the simplest processes suitable for Australian 

 ores — one adapted for the extraction of silver from ores not 

 rich enough to pay for smelting, or from ores that do not 

 easily yield to ordinary treatment — is the Joachimsthal 

 process suggested by the late Dr. Percy and Von Patera, 

 also known as Kifs' method. 



Many modifications and improvements have been made 

 OH the original process, and the names of Henderson, 

 Claudet, and others are associated with it, the modifications 

 being made to suit the great variety of ores treated. 



The ore, broken small, dried, if necessary, and crushed 

 fine under the stampers, is mixed, with or without prehminary 

 roasting, according to the nature of the ore, with 12-15 per 

 cent, of common salt, and roasted 6-10 hours. The active 

 chlorine molecule seizes the copper, lead, gold, and silver 

 molecules to form the chlorides of these metals. On now 

 soaking out the cooled product in water — the operation 

 termed leaching — a portion of the now soluble metals are 

 removed, being dissolved in the salt water. Allowing the 

 earthy impurities to separate, this liquid is drawn oft" and set 

 aside for after treatment. The roasted ore is further 

 hxiviated by means of a cold solution of 1-2 per cent, 

 sodium thiosulphate, and added to the first liquor. From 

 this the lead is removed as " white lead " by soda ash, 

 yielding at once an article of commercial value, and the 

 copper and silver are both separated out by precipitation 

 with sodium or calcium sulphide ; the product, containing 25 

 per cent, of silver, is dried and roasted, being then available 

 as a marketable commodity. This ])rocess has been suc- 

 cessfully carried out at liivertree, N.S.W., by Mr. Hall, of 



