MIXING. 245 



sluice should be near the level of the ground, and as that may 

 be steep or level below the claim, the grade of the sluice must 

 to some extent conform to it. There are thus a multitude of 

 points to be taken into consideration in fixing the grade of a 

 sluice ; but a fall of less than eight or more than twenty inches, 

 in a box of twelve feet, would be considered as unsuitable for 

 the board-sluice. Sometimes the upper part of the sluice is 

 made steeper so as to dissolve the dirt, and the lower part has 

 a small grade to catch the gold. The clayey matter of ordi- 

 nary pay-dirt is fully dissolved in a sluice two hundred feet 

 lono- with a low g-rade, so the use of the boxes bevond that 

 length is merely to catch the gold. There are claims however 

 in which the clay is so extremely tough that it will roll in 

 large balls more than a quarter of a mile through a steep sluice 

 with a large head of water, and come out at the lower end 

 scarcely diminished in size. 



The gold is caught in the sluice-boxes by false bottoms of 

 various kinds. It would not do to leave the smooth boards, 

 for the water would sweep all the gold away, and the boards 

 themselves would soon be worn throu2"h. The most common 

 false bottom is the longitudinal riffle-bar, which is from two to 

 four inches thick, from three to seven inches wide, and six feet 

 long. Two sets of these riffle-bars go into each sluice-box, the 

 box being twice as long as the bar. A set of riffle-bars is as 

 many as fill one-half of a box. They are wedged in, from an inch 

 to two mches apart ; the wedging being used, because the bars 

 can more readily be fastened in their places, and more easily 

 taken up, than if nails were used. Before the work of sluicing 

 commences, all the boxes are fitted with riffle-bars, and the 

 bottom of the sluice is therefore full of holes from one to two 

 inches wide, from three to seven inches deep, and six feet long. 

 These are the places in which the gold, quicksilver, and amal- 

 gam are caught. Quicksilver is used now in nearly all the sluices, 

 and is the more necessary the smaller the particles of gold. 

 The large pieces of the metal would all be caught by their 

 specific gravity without the aid of amalgamation. 



