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Ch. 14: Tunnels and Sluices

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TUNNELS AND SLUICES.
221
serted. The bottom and sides are spiked together gene­rally with nails four inches apart. It is not necessary to plane either the bottom or side planks. In many cases the planks are simply fitted well and closely nailed together.
The sills are placed from 3 to 4 feet apart, depend­ing upon the size of the scantling used, which is regulated by the width of the sluice; thus a 4-foot sluice would re­quire a sill 7 feet long, of 4 by 6 or 4 by 4 inch stuff. The posts are halved into the sills and firmly spiked, and every second or third post should be supported by an angle brace. The bottom planks should be solidly secured to the sills by a liberal use of heavy spikes. The bottom of a new sluice is liable to be raised by the pressure of the water which collects under it and finds no discharge. To avoid this the flume should be heavily weighted down by loading the ends of the sills with stones. In tunnels the ends of the sills can be held down by braces extend­ing to the rock overhead.
North Bloomfield Tunnel Sluice.—The annexed diagrams give the detailed construction of the tunnel sluice box used at the North Bloomfield Mine. The box is 6 feet wide and 12 feet long, with sides 32 inches deep.
To each sluice box are used :
On the outside of the tunnel the sills and braces are longer. The nails for the bottoms are 30d., for the sides 20d. The side lining, composed of worn blocks when available, is 3 inches thick, 18 to 20 inches deep, and is set 2-1/2 to 3-1/2 inches above the bottom. The riffle strips, between the blocks, are 1 1/2 by 3 inches and 5 feet 11 1/2 inches long. The blocks are 13 inches deep and 20-1/2 inches square, and average about 19 to the box. Where
Ch. 14: Tunnels and Sluices Page of 331 Ch. 14: Tunnels and Sluices
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