The floor of the sluice is laid with riffles made of strips of wood 2 in.
Air is then forced into the inclosed space by means of a compressing engine, until the pressure is sufficient to oppose the flow of water into the excavation, and to drive out any that may collect in the bottom of the shaft through a pipe which is carried through the air-sluice to the surface.
A small sluice placed in the side of the conductor opposite to the meadow, and at the upper end of it, will drain away the leakage that may have escaped from the head sluice.
Broad; it has vertical shafts at intervals, and a sluice chamber at its egress from the lake.
At neap-tide; in the sluice of the dock the numbers are 291 and 231 respectively.
And upwards in area, which are placed somewhat below the main sluice, and communicate with it above and below, the entry being protected by a grating so that only the finer material is admitted.
The incline of the sluice varies with the conformation of the ground and the tenacity of the stuff to be washed, from 1 in 16 to I in 8.
Disintegrating auriferous gravels by powerful jets of water, and the sluice system described above; in the second case the vein stuff is prepared by crushing and the amalgamation is carried out in mills.
The discharge of a river at a weir can be regulated as required and considerably increased in flood-time by introducing a series of openings in the centre of a solid weir, with sluice-gates or panels which slide in grooves at the sides of upright frames or masonry piers erected at convenient intervals apart, FIG.
It then passes through screens and grizzlies to retain the coarse gravel, the finer material passing on to sluice boxes provided with riffles, supplied with mercury.
Access to the surface is obtained through the double doors of the air-sluice, 2 N.
The barrage at the head of the Nile delta, and the regulating sluices across the Nile at Assiut and Esna in Upper Egypt below Assuan, are examples of draw-door weirs, with their numerous openings closed by sluice-gates sliding on free rollers, which control the discharge of water from the river for irrigation.
Each pair of wheels is built in three storeys, and the outflow of the water is controlled by a cylindrical gate or sluice, which is moved up and down by the action of the governor.
It is fitted with a section pipe and a circular balanced sluice for admitting and cutting off the water-supply.
A sluice surreptitiously opened during a dark night and allowed to run for six hours may quite possibly double the value of his crop, but apparently the law is not often broken.
It is first surrounded by an embankment, after which the water from the river is allowed to flow through a properly constructed sluice in its bank, along a drain or ditch to the land which is prepared for warping.
The " pan " is now only used by prospectors, while the " cradle " and " tom " are practically confined to the Chinese; the sluice is considered to be the best contrivance for washing gold gravels.
Of silt, and the field which has only one sluice can only be warped every other tide.
The " tom " is a sort of cradle with an extended sluice placed on an incline of about I in 12.
In order to save finely divided gold, amalgamated copper plates are sometimes placed in a nearly level position, at a considerable distance from the head of the sluice, the gold which is retained in it being removed from time to time.
This fric tion has been greatly re duced by making the draw doors, or sluice-gates, slide on each side against a verti A cal row of free-rollers sus pended by an encircling / chain; and the working .%i/ is much facilitated by FIG.
Of Spain caused a sluice to be built into the dock in 1567.
A sluice of 6 ft.