SOME ACCOUNT OF THE TIN MINES AND THE 



MINING INDUSTRIES OF PERAK. 



By L. Wray, Jun. 



Chapter V. 



HYDRAULIC MINING. 



Hydraulic mining, as carried on in California, is a method 

 of employing a jet of high pressure water to break down the 

 gravel or earth that contains the gold, and wash it into a long 

 line of boxes. As it passes down them the earth and gravel 

 get broken up, and the gold is caught and retained in the 

 bottom of them by becoming amalgamated with the mercury 

 which is placed there for that jiurpose. The bottoms of the 

 sluice boxes are covered in different ways with wood, iron or 

 stone, with the object of affording interstices in which the gold 

 and mercury may collect, and also to withstand the wear and 

 tear of the water, stones and gravel which, naturally, is very 

 great. 



The top part of the sluice is nari'ow and deep, with a fall 

 of one in nine or twelve, and it should be long enough to 

 thoroughly break up the clay. Then come one or more series 

 of iron bars, which are so arranged that the fine gravel passes 

 throvigh them while the stones are ejected. The lower part 

 of the sluice is wider and at a lesser grade, so as to give the 

 gold more chances of sinking and coming in contact with the 

 mercury in the bottom of the boxes between the riffle bars. 

 These are bars of iron, or wood, or iron -faced wood, set at 

 intervals either across the boxes or in the direction of their 

 length. The sluices are often over a mile in length, and some 

 tons of mercury are put into them to collect the gold. 



At intervals the current is diverted from the sluice boxes 

 proper into wide riffle -covered tables, known as under currents. 

 In these, the flow being less, the finer gold settles down between 

 the riffles and is caught by the mercury. As many as a dozen 

 of these under currents are put into some of the sluices. 



The principles involved are therefore very simple, firstly, the 

 pay-dirt has to be broken up and, secondly, the heavy portions of 

 it allowed to fall down into the spaces between the riffles, wliere 



