GOLD EXTRACTION PROCESSES. 491 



weight as silver plates, which, when dry, show the lamin- 

 ated texture of their daily augmentation." 



The knowledge of this behaviour of amalgam in the 

 Cazo process must have been common to many who were 

 engaged in exploiting the quartz veins of the West soon 

 after their discovery, and the speedy application of this 

 knowledge is exactly what might be expected from those 

 sturdy pioneers. Nevertheless, the exact date and locality 

 of the introduction of the copper plate remains a matter for 

 conjecture. 



The copper plates fixed on the battery in the early 

 fifties were about four inches wide and as long as the 

 mortar, and were placed one on the "feed" side and one 

 on the discharge side just underneath the screens. It 

 was soon found that the plates worked better from the 

 start if mercury was rubbed on them before they were 

 placed in position, and this has now been invariably done 

 for many years. Crushed ore, stones, water, and amalgam 

 are flung violently against the plates and the amalgam is 

 retained in great part. 



The scouring action of the pulp on the plates is however 

 always great, and becomes more violent in proportion as 

 the stamps are larger. These are now as much as 1100 

 and even 1250 lbs. in weight in the Transvaal, an enormous 

 mass when compared with the 750 lb. stamp of a few years 

 ago, and the 1 20 lb. stamp of the last century. With this 

 increase in weight, it has become desirable to modify the use 

 of the copper plate. The plate on the feed side, long ago 

 condemned by many, is accordingly being discarded more 

 and more, and that below the screens is curved away in such 

 a manner that it cannot be struck directly by the splash 

 from the stamp, while slots in cast-steel plates lining the 

 mortar have been devised for the purpose of catching 

 amalgam. 



After leaving the mortar the pulp was treated forty 

 years ago mainly by passing it over inclined tables covered 

 with blankets, much in the same way as Jason may have 

 seen the golden sands worked in Asia Minor. The sands 

 accumulating on the blankets were washed off at intervals 



