248 BESOUECES OF CALIFORiNIA. 



being lost. The greater the quantity and proportion of fine 

 gold, the greater the importance of the quicksilver. ' 



The best method of catching very fine gold by amalgama- 

 tion is to cover a large copper plate with mercury, and let the 

 dirt and water, in a thickness of not more than a quarter of an 

 inch, pass over it slowly. There are various methods of cover- 

 ing copper plates with quicksilver. The first thing, in every 

 case, is to wash the copper with diluted nitric acid, so as to 

 remove all dirt and grease. The quicksilver may then be 

 rubbed on with a rag ; or, still better, it may be dissolved in 

 nitric acid, and the liquid nitrate of quicksilver may be applied 

 with a rag. The nitric acid will attack the copper, and leave the 

 quicksilver as an amalgam on the surface of the copper. This 

 is the most common process, but the nitrate of copper con- 

 tinues for a long time to come up through the quicksilver and 

 interfere with the catching of the gold. When the nitrate of 

 copper appears — it is a green slime — it should be scraped oflT 

 and the place rubbed over with quicksilver. When a plate is 

 once covered with mercury, the operation need never be re- 

 peated ; but more mercury must be sprinkled on as the gold 

 collects and forms a solid amalgam. The plate is usually three 

 feet wide and six feet long, and is set nearly level. In very 

 large sluices the stream should be divided so as to run over 

 different plates. The slowness of the current and the shallow- 

 ness of the water are important, for with a swift current or 

 deep water many of the particles of float-gold may escape 

 without touching the quicksilver. Wherever a speck of gold 

 has fixed itself on the plate, there others will collect about it, 

 evidently preferring to fix themselves in a neighborhood rather 

 than in a waste place. The more gold there is on a plate, the 

 better it is considered to be. The seasons for cleaning up are 

 usually determined by the danger of theft. Miners do not like 

 to leave their gold out in quantities so large as to attract 

 thieves. The amalgam is sometimes half an inch thick, and 

 is usually, at cleaning-up time, a hard mass, which must be 

 loosened by heat. The plate is put on a fire, and when it gets 



