248 RESOURCES OF CALIFORNIA. 
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 thickuess 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 
1ubbed 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 off 
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 
