purington.] SLUICES AND GOLD-SAVING APPLIANCES. 201 
in gangs of four, and that a locking device is employed to prevent the 
gangs from coming up. Rail riffles of this kind are primarily intended 
for hydraulic operations and give excellent satisfaction, but can be 
recommended for creek placers only where the capacity warrants 
expensive installation. 
At the present day the saving of fine gold is receiving marked 
attention on gold dredges, as the product of these machines frequently 
consists largely of gold in an exceedingly fine state of division. 
Fig. 42 and PI. XXXVII, B, represent a sluice table now in use at 
Oroville, Cal. The grade of the table on the dredge at Atlin, British 
Columbia, is 12 per cent, corresponding nearly to 18 inches to 12 feet. 
These tables are set transversely beneath the main sluice, which is fed 
directly from the trommel, the main sluice having a grade of 12 inches 
to 12 feet. The quicksilver charge of the sluice and table is 200 pounds. 
The largest material passing over the sluice is 4 inches in diameter, 
while grizzlies do not permit over-J-inch sizes to go over the undercur- 
rent tables. The total area of sluices and tables is from 600 to 1,000 
square feet, from 500 to 700 miner's inches of water being used for an 
amount of material which will probably average 1,500 cubic yards per 
twenty-four hours. 
The type of riffle here figured is used extensively at Oroville at 
present. It is stated by one of the operators who has experimented 
with the gold in that field, that from 15 to 20 per cent of the gold 
recovered with quicksilver, using this riffle, will pass 150-mesh sieve. 
The expanded metal and cocoa matting riffle is also used with suc- 
cess at Oroville. 
The Oroville gold contains a much larger proportion of fine colors 
than the northern fields. From the undercurrent sample of Klondike 
gold above described, assuming that this represents 5 per cent of the 
total recovery, screening tests appear to indicate that under 1 per 
cent of the Klondike gold, and under 2 per cent of the Fairbanks 
Creek gold, will pass 150 mesh. 
The fineness of the gold on Sulphur Creek is shown by the tabic 
below : 
Fineness of gold from Sulphur Creek. 
Mesh. Per eent. 
Under 150 10 
150-100 00 
100-80 20 
80-60 10 
Moreover, the gold, whatever its fineness of division, is generally 
round and shot-like and not flaky. Under such conditions, in view of 
the Oroville experience, losses such as undoubtedly occur in the 
northern practice are inexcusable. 
The riffle shown in fig. 46 is designed to hold a divided sheet of 
quicksilver. Another form is made by boring 1^-inch augur holes to 
