GOLD IN SCIENCE AND IN INDUSTRY. 217 



costly mining appliances, and where the precious metal was loosely 

 associated with a weathered matrix. These free-milling ores could 

 be readily handled by crushing and amalgamation with mercury, so 

 that here also no elaborate organization and no great expenditure 

 of capital were necessary. A third stage w^as reached when the more 

 easily worked deposits above the water line had been worked out. 

 Not only were more costly appliances and more elaborately organized 

 eiTorts required to bring the ore to the surface, but the ore when 

 ol)tained contained less of its gold in the easily recovered, and more 

 in the refractory or combined form. The problem of recovery had 

 now to be attacked by improved mechanical and chemical methods. 

 The sulphides or tellurides with which the gold was associated or 

 combined had to be reduced to a state of minute subdivision by more 

 perfect stamping or grinding, and elaborate precautions were neces- 

 sary to insure metallic contact between the particles of gold and the 

 solvent mercury. In many cases the amalgamation process failed to 

 extract more than a very moderate proportion of the gold, and the 

 (juartz sand or '' tailings " which still contained the remainder found 

 its way into creeks and rivers or remained in heaps on the ground 

 around the batteries. In neighborhoods where fuel Avas available a 

 ]5reliniinary roasting of the ore was resorted to, to oxidize or volatilize 

 the baser metals and set free the gold; or the sulphides, tellurides, etc., 

 were concentrated by washing, and the concentrates Avere taken to 

 smelting or chlorinating works in some favorable situation where the 

 more elaborate metallurgical methods could l)e economically applied. 

 Many efforts were also made to apply the solvent action of chlorine 

 directly to the unconcentrated unroasted ores; but unfortunateU" 

 chlorine is an excellent solvent for other substances besides gold, and 

 in practice it was found that its solvent energy was mainly exercised 

 (•n the base metals and metalloids and on the materials of which the 

 i:i)paratus itself was constructed. 



This to the best of my knowledge is a correct, if rather sketchy, 

 description of the state of matters in 1889 when the use of a dilute 

 solution of cyanide of potassium was first seriously proposed for the 

 extraction of gold from its ores. Those of us who can recall the time 

 ■will remember that the proposal was far from favorably regarded 

 from a chemical point of view. The cost of the reagent,' its extremely 

 ])oisonous nature, the instability of its solutions, its slow action^ — 

 such were the difficulties that naturally presented themselves to our 

 nnnds. And, even granting that these difficulties might be overcome, 

 there still remained the serious prolilem of how to recover the gold in 

 metallic form from the extremely dilute solutions of the cyanide of 

 gold and j)otassium. How each and all of these difficulties have been 

 swept aside, how within little more than a decade this method of 

 SM 1905 18 



