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An experiment at the Empire Mill, French Corral, was made under the following circumstances, giving the annexed results: Ten stamps, weight of each 6934 lbs. Drop, .768 feet. Speed of stamps, 62.2 drops per minute. Work done by 91.68 cubic feet of

water per minute. Head, 130.1 feet. Size of wheel, 131 feet outer diameter. Diameter of wheel, 12.58 feet to centres of buckets. Size

of buckets, 4 inches wide and 6 inches deep, set 10 inches apart. Water conducted to wheel through an 11-inch pipe 866 feet long. The wheel was direct on the cam-shaft; single cams used. The mill crushed sixty tons of gravel in twenty-four hours; inch screens used.

The head at French Corral was the height of the water in pen stock above the nozzle, no allowance being made, as was the case in

the Bloomfield experiments, for loss of head by friction in pipes and

some leakage.

STATISTICS OF YIELD OF GRAVEL-FIELD.

Statistics showing the quantity of material washed, and the corresponding yield in gold, are rare, difficult to obtain, and for the most part unreliable. This is due principally to the fact that, in the early days of placer mining in California, the question to be solved by the miner was not what the gravel would yield per cubic yard, and what it would cost to move it, but rather how many ounces of gold dust he could "pan out" or "rock out" between sunrise and sunset. All that he required was that the daily yield in dust should exceed the cost of living, etc. When it fell below this, he moved his camp to other grounds.

The wonderful productiveness of the river bars and shallow placers, attested by the early gold bullion and dust shipments from this State, created an extravagance usual to all new and rich mining countries, the baneful effects of which are still visible. Gold in such profusion is no longer found so conveniently scattered. The introduction of hydraulic mining requiring the assistance of capital has inaugurated a new era in gravel-washing. Hence all data of the yield and costs of working gold-bearing surface deposits become valuable, and accordingly the following tables have been added:

Table I. Showing the Yield of Gravel per Cubic Yard at Various Hydraulic Claims.

Indiana Hill,*.

Remarks.

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HYDRAULIC MINING IN CALIFORNIA.

H. Smith, Jr..
Ray, Rep., 1874......

W. K. Conger.........
Cooper....

H. W. Wallace....

"

Henry C. Perkins.

Estimated by several engineers, Ray. Rep., 1874, p. 19.

Raymond's Report, 1874.

Calculated from data, p. 84.

"

Gravel worked in a mill. Cubic yards estimated from
coarse dirt in cars, p. 100.

Deep placer mining; gravel extracted and then sluiced.
Cubic yards estimated from coarse dirt.
From June 24th, 1875, to June 24th, 1876, 100,080 car-
loads of gravel mined, stripping 300,240 superficial
feet of bed-rock. Each car contained 1 cubic yard
of loose gravel 1⁄2 cubic yard of gravel in place.
Year ending June 24th, 1877, 98,044 car-loads extracted,
stripping 343,768 superficial feet of bed-rock.
Calculated from data in Raymond's Rep., 1872.

Cement claim.

"

84

The richest gravel selected and milled.

Top gravel.

Upper bench gravel.

This ground was washed in 176 days and five hours, ending August 3d, 1877. The yield includes the top and bottom gravel.

J. Rathgeb...

2,268

1,560.00

68.5

122

HYDRAULIC MINING IN CALIFORNIA.

2.46

Cu. yd. in gms.

Shallow spots.

Virgin ground.

Drifted in placer.

Virgin ground.

Virgin ground.

* Italics denote mines not worked by the hydraulic method.

95