SILVER MINING IN COLOEADO. 621 



struction of this macliine, or, more correctly, of two machines, which, for 

 conveaience, are put together as one, though quite independent of each other 

 in their operation. A double machine, like that shown in the drawings, con- 

 sists of a box or tank, about seven feet long and between three and four feet 

 wide, divided by a middle partition, as shown in Fig. 1, into two parts. 

 Each of these parts is fitted on the inside with inclined partitions, sloping 

 from the four sides toward the center of the box, as shown in Figs. 1 and 2, 

 and thus forming two cisterns, C, above each of which is placed a sieve, h. 

 The sieve-frame may be furnished with a wire-cloth sieve of any desired 

 degree of fineness, according to the character of the ore to be dressed. Be- 

 tween the two sieves are the piston or plunger-compartments, e, separated 

 from each other, and each connecting by an aperture, /, with one of the cis- 

 terns, C. Each aperture,/, affords communication with the cistern nearest 

 to it, but without any connection with the other cistern. The plungers, c?, 

 move up and down in the compartments, e, being forced rapidly downward 

 by rockers, ^, and lifted again by the action of springs, p. The rockers are 

 set in motion by pulleys, /<;, with which they are connected by eccentric 

 rods, /. The cisterns and plunger-compartments are supplied with water by 

 pipes, g, and when the outlets, o, are closed the machines are filled with 

 water, the overflow being at q, in front of the sieves. The movements of 

 the plungers, therefore, which follow each other in rapid succession, produce 

 an agitation of the water, which rises through the sieves with a constantly 

 throbbing motion. The crushed ores, consisting of heavy mineral and gangue, 

 are brought upon the sieves, h, by a stream of water that enters through the 

 distributing boards, c, and being subjected to the agitation caused by the 

 plungers, d^ are held in a state of partial suspension, during which the heavier, 

 metallic particles sink, while the earthy matters rise to the top and are 

 carried off" by the water at the overflow, q. That portion of the metalHc 

 substance which is fine enough to pass the meshes of the sieve falls through 

 into the hutch or cistern, C, and may be withdrawn thence at stated intervals 

 by the outlet pipe, o; while the coarser part remains upon the sieve and is 

 cleaned up from time to time, leaving a stratum on the sieve for continued 

 operations. The thimbles, r, on the plunger rods, p, serve to adjust the 

 length of the stroke. The action of these machines is excellent. They effiecl 



