120 THE PROSPECTOR'S HANDBOOK. 



To assay Copper ores by the crucible method, includ- 

 ing the refining process, requires much practice, and for this 

 reason the " wet assay " is the more suitable for obtaining 

 an approximate estimation of the amount of metal in a 

 copper ore. 



Assay of Tin Ore. 



If the ore be poor, it ought to be concentrated, the vein- 

 stuff being got rid of as much as possible. If mixed with 

 iron or copper pyrites, it ought to be calcined or else treated 

 with acids. One method is, as in Cornwall, to mix the ore 

 with one-fifth of its weight of anthracite coal or charcoal, 

 and to expose it in a crucible to a great heat for about 

 twenty minutes. The contents are then poured out into 

 an iron mould, and the slag carefully examined for buttons. 



Another method is to mix 100 grains of the ere with six 

 times its weight of cyanide of potassium, and expose the 

 mixture to the heat of a good fire for twenty minutes. The 

 contents are allowed to cool, and afterwards broken to 

 remove the slag. The buttons are then weighed. 



To assay Mercury ores, see MERCURY, Chapter V. 



Antimony. 



To determine the amount of antimony in an ore 

 containing sulphide of antimony and more or less vein- 

 stuff : 



Place about 2,000 or more grains of broken-up ore in a 

 crucible, the bottom of which is perforated, and the hole in 

 which is partially closed by a small piece of charcoal. Now 

 fix the bottom of this crucible into the mouth of another 

 crucible, so as to be about half-way down its depth. Then 

 lute* the lid and also the joint between the two crucibles 

 with fireclay and sand. By placing the lower crucible 

 under the furnace bars and the upper one above, the heat 

 of the furnace will cause the sulphide of antimony, which 

 fuses at a red heat, to collect in the lower crucible, while 

 the quartz and other matter will remain in the upper one. 

 The operation should take about an hour and a half. 



* A dough of fresh fireclay and ground firebricks is a good lute. 



