LEAD AND SILVER. 13 3 



and disseminated ore are carried to the stamps and washing-flooi 

 to be treated separately. As much of the gangue as can be removed 

 is thrown away. The lean ores are usually crushed by hand. 

 but mechanical devices are sometimes used. It is a custom in 

 China as in most other Eastern countries to extract ore in the 

 mines by heating the faces and then suddenty quenching them. 

 This has the effect of rendering them more amenable to subsequent 

 crushing than would be the case otherwise. 



The stamp used is made on the same principle as the ordinary 

 Chinese overshot watenvheel used for husking rice. Two heavy 

 bars of wood are let in at right angles into the axle on both sides 

 of the wheel. They are so arranged that as the wheel revolves 

 they strike alternately heavy wooden beams which are poised as 

 levers, by being supported at about two-thirds of their length. 

 The blow delivered on one end of the beam depresses it and 

 lifts up the other end. To the latter end a pestle is attached, 

 made of wood as in the case of a rice mill, but fitted with a 

 heavy iron shoe when stone is to be crushed. The pestle falls 

 into a mortar in which the pieces of ore are placed. A strong 

 stream of water carried in a box to the wheel serves to drive 

 this rough but none the less useful machine. 



The washing and concentration of the roughly pow T ered ores is 



performed bv the following processes. A 

 ^Washingandconccn- gtream of ^^ ^ directed a , Qng ft genf j y 



inclined wooden sluice-box some 12 feet Urns 



2 feet broad at one end and about 1 foot deep; it narrows slightly 



at the other end and has a removable riffle a few inches high. 



Beyond the box the water flows into a series of settling tanks. 



After placing the crushed ores in the box, the water is directed 



on to them and concentration done by a workman with a rake 



in the usual way. Fines escape into the tanks, which are cleaned 



up and their concentrates worked out from time to time. 



A fairly high-grade lead ore is obtained by these methods, for 



no hesitation is shown in rejecting material 

 Preliminary roasting. , . . ,,. ... _" , 



showing any metallic impurities which would 



interfere with the subsequent smelting. Copper, antimony and 



zinc ores are removed in the hand-picking, gangue is removed by 



washing. The fact that the methods employed in lead-smeltinc 



vary little from place to place even over widely separated areas. 



although the association of other minerals with the lead ores alters 



