580 MINING INDUSTET. 



The roasting of the ore in heaps, or mounds, is a slow but comparatively 

 cheap process. A single heap usually contains some 30 or 40 tons of ore 

 and requires five or six vi^eeks for the operation. In preparing it, a bed of 

 cordwood, about 16 feet square, is Jaid as the base of the pyramid that is to 

 be composed of ore. Directly upon the ground a course of thick billets of 

 v^^ood is laid, the sticks being parallel, but at a little distance apart, so as to 

 permit the passage of a current of air. Above this, other courses of vv^ood are 

 laid more closely and crossvv^ise, forming a bed about 5 or 6 inches thick, requir- 

 ing altogether about a cord of wood for a single heap. A wooden chimney, 

 or box flue, 9 or 10 inches square, is set up vertically in the center, passing 

 down through the bed of fuel and reaching above the top of the heap. A 

 small quantity of charcoal is put in at the bottom of this box or chimney, and 

 the heap is ignited, when ready, by setting fire to the coal. The ore is formed 

 into a heap about 4 or 6 feet high on this foundation and around the central 

 chimney. The larger pieces are placed on the inside and the whole covered 

 on the outside by a layer of fine stuff. This is so disposed as to control the 

 rate of combustion, promoting it, if too slow in any part, by opening a pas- 

 sage for the draught, or checking it, if too rapid, by covering more closely. 

 The heaps, when burning, require only sufficient attention to insure a proper 

 rate. If allowed to burn too rapidly, the ore slags; or, if too slowly, the cal- 

 cination is imperfect and the fire may go out altogether, requiring rehandling, 

 with a loss of time and money. To break the ore, weigh it, wheel it to the 

 yard, and lay it up in heaps, costs $2 30 per ton. 



Tailings, owing to their fine condition, cannot be roasted in heaps, and 

 must be treated in calcining furnaces, of which there are two. They are 

 about 30 feet long by 10 feet wide, inside. The fireplace, separated from 

 the hearth by a bridge about 15 inches high, is at one end of the furnace; 

 the flue at the other end. The bottom of each is flat, and is a single course 

 of common brick laid on a solid stone or rubble foundation. It is laid as 

 three hearths, on slightly different levels ; the first, about one-third of the 

 total length, and most remote from the fireplace, is about 4 inches higher 

 than the middle, which, in turn, is about 4 inches higher than the remainder, 

 next the fireplace. The sides of the furnace are little less than 2 feet high, 

 and the top is sfightly arched over from side to side. In one side of the 



