86 TIN MINING IN PERAK. 



of the stream of water, and also the distance to which it will 

 carry. The rifling, as these ribs are most inappropriately called, 

 is therefore a very important portion of the monitor. 



The jet in use at the time of the writer's visit to the mine 

 was one and a half inches in diameter, but a two -inch nozzle 

 could be used with the supply of water available, a:id after 

 some slight alterations had been made in the sluice it was 

 possible to use the two -inch jet. This gives two and a quarter 

 times as much water as the one and a half inch jet, and con- 

 sequently will deal with that amount more of wash -dirt. 



In working, the jet is directed against the bank of earth, 

 which rapidly breaks dovni under the impact of the stream, 

 and is carried l)y it into a ditch leading from the working face 

 to the head of the sluice boxes. The length of this ditch varies 

 from day to day as the work proceeds. From it the water and 

 dirt flow into a narrow sluice box set at a steep grade. The first 

 series of boxes is fifty feet in length by ten inches wide by ten 

 inches deep, and the grade is about one in six. Next in order 

 come fifty feet of boxes, twenty inches wide by ten inches deep, 

 set at one in ten ; then a hundred feet of boxes, thirty inches 

 wide with a grade of one in twenty. Inside some of these are 

 zigzag riflies, the office of which is to throw the water and gravel 

 violently from side to side in the boxes and disintegrate the 

 clayey portions of it. At the end of this line of boxes comes 

 a drop of five feet ; that is the water falls sheer down from 

 one box into another placed five feet below it. The object 

 of this is to further break up the earth and liberate the tin. 

 Beneath the drop and extending at right angles to it are twenty- 

 five feet of thirty -inch wide boxes, and at the end of them a 

 " grizzley " (that is a slanting grate of iron bars so arranged as 

 to throw out the stones) and a second drop of six feet. At 

 the bottom of this the sluice is widened out to forty inches, 

 and the grade lessened to one in twenty -four. These latter, 

 termed wash boxes, are fifty feet in length, and their object is 

 to catch the tin -sand, as will be explained further on. At 

 the end of these five boxes the sluice narrows again to thirty 

 inches, and the grade increases to one in eighteen. There are 

 eighty feet of these boxes, and they are furnished with trans- 

 verse riflie bars of three by two and a half inch wood, fixed 

 at intervals of twelve inches apart. Sixty feet of similar boxes, 

 also furnished with riffle bars, follow these on a grade of one 

 in twenty -four. Lastly come fifty feet of fifty -inch wide wash- 

 boxes, at a grade of one in twenty -four. These, like the wide 

 ones higher up the sluice, are employed to save the tin -sand. 



Following the sluice boxes is a tail-race of half a mile 



