134 COGGIN BROWN : MINES & MINERAL RESOURCES OF YUNNAN. 



much in different localities, is sufficient fco show that considerable 

 care is taken in the preliminary concentrating processes. The 

 Chinese profess to be able to tell from the lustre and structure of 

 a particular galena, whether its silver content is high, low or medium. 

 The ores of a fine granular appearance, compact and massive, and 

 exhibiting glittering facets on the broken surface of a fractured 

 specimen are considered to be the richest in silver. 



Lead is usually produced in Yunnan by a " roast and reduc- 

 tion " method, but the Chinese are also acquainted with a "roast 

 and reaction " method too. I have not seen this method in actual 

 operation in Yunnan but it was employed on a very large scale 

 at the Bawdwin mines of the Northern Shan States', as the remains 

 of the old furnaces and composition of the slags proved. 



The powdered ores are burnt in stalls, which consist simply 

 of three brick walls, forming the three sides of a square four or 

 five feet across, the fourth side being left open. Several of these 

 are arranged in a row. The ore is stacked on a charcoal bed and 

 alternate layers of ore and charcoal are added. After ignition, 

 the mixture is allowed to burn slowly for several days, charcoal 

 or even wood being added to keep combustion going as required. 

 During this roasting the material agglomerates and when cool it 

 has a porous, sintered appearance. If the ores have not been 

 carefully selected, it is the custom to smash up the roasted mass 

 and to concentrate it in the sluice-boxes already described. The 

 operation of roasting is repeated four times, at the end of which 

 most of the lead compounds appear to be in the form of oxides. 

 Careful attention is paid to the ventilation and temperature of 

 the roasting so as to prevent the formation of sulphates as far as 

 possible and to obviate reduction to metallic lead. 



The furnace used for smelting lead ores is from seven to nine 

 „ , . feet high, made of brickwork and lined 



Smelting. . . ° p , . • . _ 



with a refractory material. Ihe side walls 

 vary greatly in thickness from place to place, but are always con- 

 structed in a massive manner so as to allow of the escape of as 

 little heat as possible. The well of the furnace is roughly square 

 in section with the corners rounded off, but it swells out into a 

 funnel shape towards the top, to permit of easy charging. I have 

 always seen charging done from the top of the furnace and not 

 from a special door as described by some writers. The outer 

 wall is roughly semi-circular in section and the back and 



