GENERAL TREATMENT OF ORES. in 



conducting the operations, and in these the powdered ores, 

 with or without fluxes, are exposed to heat in a furnace, the 

 temperature varying according to the nature of the ore. 



The principal fluxes employed are : 



Carbonate of Soda, or Potash, which forms fusible 

 compounds with silica, &c. 



Borax, which forms fusible compounds with lime, oxide 

 of iron, &c. 



Glass, Silica, Fluor-Spar, Litharge, and others. 



Reducing Agents are used, such as charcoal powder, 

 cyanide of potassium. 



Oxidizing Agents, such as atmospheric air (removing 

 sulphur, &c., in the roasting process), nitre (which is very 

 rich in oxygen), litharge, salt, &c. 



Desulphurizing Agents (for removing sulphur), such 

 as air (in the roasting process), iron nails, carbonate of 

 soda, &c. 



Agents to remove Arsenic, such as atmospheric air 

 (in roasting process), nitre, &c. 



Collecting Agents (for collecting silver or gold), such 

 as lead, mercury, &c. 



GENERAL TREATMENT OF ORES. 



Specimens to be assayed should not be chosen to elicit a 

 "good assay" only. They should represent dressed ore 

 ready for shipment. When an average portion of rock has 

 been selected, it should be carefully powdered, if possible, 

 in a mortar, or, in the absence of a mortar, broken up into 

 a few pieces; and these, rolled up in cloth or paper, should 

 be powdered between two hard rocks. To prevent frag- 

 ments from flying out of the mortar, a loose paper cover, 

 with a hole in the centre for the pestle to pass through, will 

 suffice. Some substances, especially those of a quartzy 

 nature, will be rendered easier to crush by first being heated 

 and thrown into water. If the ore does not contain metallic 

 particles, the operation of powdering and sieving is compa- 

 ratively easy ; when, however, metallic fragments are mixed 



