“Screens of different materials and with different orifices are used; the materials comprise wire cloth of brass or steel, tough Russian sheet iron, English tinned plate, and, quite recently, aluminium bronze. The ‘aluminium bronze’ plates are much longer lived than either of the other kinds, and have the further advantage that, when worn out, they can be sold for the value of the metal for remelting; these plates are bought and sold by the pound, and are said to contain 95 per cent of copper and 5 per cent of aluminium. Steel screens are not so much used, on account of their liability to rust.”
I have had no experience with the aluminium bronze screen. I presume, however, that it is used only for mills where mercury is not put in the mortars, otherwise, it would surely become amalgamated. The same remark applies to brass wire cloth and tinned plate. Unless the metal of which they are composed will not readily amalgamate with mercury, I should be chary of using new screen devices. Mercury is a most insidious metal and is often found most unexpectedly in places in the battery where it should not be. Probably aluminium steel would be better than any substance mentioned. It would be hard, light, strong, and not readily corrodible. I am not aware if it has been tried.
Under the heading of “Power for Mills” the following is taken from the same source.
“As the Pelton wheel seems to find the most frequent application in California, it may be convenient for millmen to have the following rule, applicable to these wheels:
“When the head of water is known in feet, multiply it by 0.0024147, and the product is the horse-power obtainable from one miner’s inch of water.
“The power necessary for different mill parts is:
For each 850lb. stamp,
dropping 6 in. 95 times per minute,
For each 750lb. stamp, dropping 6 in. 95 times per minute,
For each 650lb. stamp, dropping 6 in. 95 times per minute,
For an 8-inch by 10-inch Blake pattern rock-breaker
For a Frue or Triumph vanner, with 220 revolutions per min.
For a 4-feet clean-up pan, making 30 revolutions per min.
For an amalgamating barrel, making 30 revolutions per min.
For a mechanical batea, making 30 revolutions per min.
The writer has had small practical experience of the working of that excellent hydraulic motor, the Pelton wheel, but if by horse-power in the table given is meant nominal horse-power, it appears to be high. Working with 800 cwt. stamps, 80 blows a minute, one horse-power nominal will be found sufficient with any good modern engine, which has no further burden than raising the stamps and pumping the feed water. It is always well, however, particularly when providing engine power, to err on the right side, and make provision for more than is absolutely needed for actual battery requirements. This rule applies with equal potency to pumping engines.