136 C0GG1N BROWN : MINES & MINERAL RESOURCES OF YUNNAN. 



top of the dome, is placed the grating which supports the fire. 

 The grating is made from a mixture of refractory sand with sufficient 

 clay to keep it together. From the upper door the charcoal tor 

 firing can be placed on the grating. The dome is made of double 

 brickwork and is lined with a refractory material. After the 

 fire is lighted and the furnace well wanned, the lead to be Cupelled 

 is placed on the hearth, where it soon melts. A bridge of sand 

 is built across the charging door to form a side for the bath of 

 molten metal and to prevent it flowing out. The fire is kepi 

 going by the introduction of more charcoal, which has to be 

 placed very carefully across the somewhat flimsy grating. As 

 the temperature rises litharge commences to form, and when suffi- 

 cient has accumulated it is removed by the introduction of an 

 iron rod to which layer after layer of the litharge sticks as it is 

 skimmed away. Sticks of stratified litharge, hollow down tin* 

 centre are sometimes found on old Chinese slag heaps. I have 

 come across them both at Bawdwin and in Yunnan. Nothing 

 now remains but to keep the operation going by regulating tin; 

 fire and removing the litharge as fast as it is formed. The process 

 is a very tedious one and is prolonged sometimes for two days 

 and nights. The silver which remains is far from pure and has 

 to go through the hands of a refiner before it can be used as bul- 

 lion. I understand that the Government insisted on a purity 

 of 98 per cent. The litharge is either sold as such or is resmelted 

 with charcoal in the ordinary way. Owing to the somewhat 

 rough treatment which the furnace undergoes, there is nothing 

 much left but the outside walls and it has to be practically rebuilt 

 inside before another cupellation can be undertaken. 



Rocher has described the refining of the silver, an operation 

 which I have not seen myself. The follow- 

 ing notes are taken from his account of the 

 process. The cake of silver from the cupel is sent to the refiner 

 whose duty it is to bring it up to standard. The operation is done 

 in an ordinary forge, the silver being melted in a crucible with 

 powdered wood charcoal. As soon as the metal is molten, and 

 the surface bubbles, two workmen are placed on each side of the 

 forf*e and it is their duty to blow down long iron tubes on to 

 the surface of the fused metal. Under the action of the oxygen 

 the surface of the metal becomes covered with a layer of black- 

 oxidised scum, which is removed as soon as it is formed. During 



