60 president's address — SECTION B. 



greatly militated against its commercial application, as did 

 the polarisation caused by the evolution of hydrogen from 

 the decomposition of the water present. To overcome these 

 difficulties, the porous partition of the decomposing tank is 

 reduced in size, and copper oxide is introduced to enable the 

 hydrogen to combine with its oxygen, thus leaving behind 

 metallic copper, which is re-oxidised by heating in a current 

 of air and used over and over again. The process may 

 obviously be used in the manufacture of caustic soda and 

 sodium hypochlorite as well as chlorine, according to 

 requirement. 



The economical production of caustic soda would enable 

 other wet processes to be used, such as Ellershausen's wet 

 process for the extraction of the precious metals from zinc 

 ores. These latter give rise to grave difficulties in many 

 parts of New South Wales, notably at the Barrier Ranges ; 

 in many cases the zinc is lost to the community for want of a 

 suitable process of extraction. The method I refer to is one 

 which can be economically worked in connection with the 

 caustic soda manufacture. The zinc ore is mixed with 25 

 per cent, of galena, if it does not already contain that quantity 

 of galena, and after being crushed, is put in a reverberatory 

 furnace and heated to a red heat, when from 35 to 50 per cent, 

 of caustic soda (the crude refuse from the soda works) is added. 

 The whole mass fusing, the galena readily gives up its sulphur 

 to the soda, and metallic lead is produced, which, with the gold 

 and silver, sinks to the bottom, the sulphides of iron, copper, 

 and zinc remaining in the slag. The lead is drawn off and 

 cupelled, and the slag, on exposure to the air, rapidly 

 crumbles to powder owing to the caustic soda present, which 

 is afterwards removed by lixiviation, and can be used over 

 again, while the metallic sulphides can be treated by the usual 

 methods. The ore should previously be concentrated to 

 remove quartz, as the soda would be wasted in forming sili- 

 cate of soda and not recoverable. The late Mr. Wilkinson, 

 my lamented friend, who drew my attention to this interesting 

 process, held the opinion also that the ores of Broken Hill, 

 Moruya, and Castle-Rag could be successfully treated in this 

 way. 



In addition to the many forms of chlorinating processes, 

 there remains for me to mention another, the principle of 

 which is that the sulphur present in many sulphide ores may 

 be subjected to a particular degree of oxidation in a reverbera- 

 tory furnace, whereby the soluble sulphate of silver is formed ; 



