DRESSING OF ORES 



77 



These fragments are but moderately rich in metal, and are picked up at random, of 

 various sizes, from that of the fist to a grain of dust. 



The ores are placed in the chest a, below the level of which 7 grates are distri- 

 buted, so that the fragments which pass through the first, b, proceed by an inclined 

 conduit on to the second grate c, and so in succession. (See the conduits /, o, p.) 

 In front, and on a level with each of the grates b, c, d, &c., a child is stationed on one 

 of the floors, fixed opposite to them. 



A current of water which falls into the chest a, carries the fragments of ore upon 

 the grates. The pieces which remain upon the two grates b and c, are thrown on the 

 adjoining table v, where they undergo a sorting by hand ; there the pieces are classified, 

 1, into gangue to be thrown away; 2, into ore for stamping mill ; 3, into ore to be sent 

 directly to the furnace. The pieces which remain on each of the succeeding grates, 

 d> c,f,g, , are deposited on those of the floors 3 to 7, in front of each. Before every 

 one of these shelves a deposit-sieve is established (see t, w), and the workmen in 

 charge of it stand in one of the corresponding boxes, marked 8 to 12. The sieve is 

 represented only in front of the chest h, for the sake of clearness. 



Each of the workmen placed in 8, 9, 10, 11, 12, operates on the heap before him; 

 the upper layer of the deposit formed in his sieve is sent to the stamping-house, and 

 the inferior layer directly to the furnace. 



As to the grains which, after traversing the five grates, have arrived at the chest x, 

 they are washed in the two chests y, which are analogous to the German chests. The 

 upper layer of what is deposited in y is sent to the furnace ; the rest is treated anew. 



The kiln before adverted to is explained by jig. 643. 



043 



The vein-stuff is brought from the shaft by means of tram waggons, into the 

 hopper A ; water flows from the launder B, one portion distributing itself at the foot 

 of the hopper, the other upon a cast-iron plate perforated with holes 1^ inch diameter 

 at top, 1 inch diameter at bottom, and 2 inches distant from centre to centre ; the 

 plate being 4 feet by 3 feet 6 inches. Between c and E, the washer stands. The fine 

 stuff he rakes through the plate-holes, and that which is too coarse is drawn to E. 

 Children standing on H, select the prill and dradge from the pile E, discharging such 

 stones as are valueless through the shoot F, into the waggon beneath. The trommel 

 D is constructed of perforated plates, having different degrees of fineness, in order to 

 size the stuff which passes through into bins or compartments. 



The washing arrangement shown in jfop. 644 is in use atPrzibram. The stuff is first 

 introduced into a shoot, from whence it passes into a conical trommel, and is thence 

 thrown upon aflat sieve, and divided into coarse and fine stuff, the former going to the 

 rotative table, the latter to sizing sieves. The shoot at the entrance of the trommel is kept 

 in movement by a cam shown underneath: the trommel rotates on carrier wheels, whilst 

 circular motion is given to the picking table by means of a tangent wheel and screw. 

 The inside of the trommel is fitted with ledges for lifting and dropping the stuff, water 

 being continually introduced for washing and freeing it from slime and clay. A rose 

 jet of water flows on the table for rendering the ore and waste more distinct to the 



