572 ]\nNING IKDUSTET. 



is increased by screwing the spring up closer to the frame, or diminished by- 

 withdrawing the screw.^ 



The distributing board, t, is divided into four parts, or aprons, for each 

 single table, each of which aprons is provided with a group of distributing 

 points. The material for concentration is supplied from a trough, u, and 

 enters the table by the apron t' . Clear water, of which a supply is kept in 

 the box w, the surplus flowing off through w' , is furnished thence, through sep- 

 arate cocks, to the aprons f, f, and f, and thus distributed evenly over the table. 

 In the manipulation of this table the following conditions are important: The 

 surface of the table must be made as smooth as possible. The width of the 

 apron from which the material for concentration is supplied to the table should 

 not exceed 8 or 12 inches, clear water being distributed over the remainder. 



^In the improved arrangement, motion is imparted to tlie table in a somewhat dif- 

 ferent manner, the cam acting directly ui)on the frame instead of by the means shown 

 in Fig. 1; and drawing the table to one side and then releasing it for the movement in the 

 opposite direction, by which it receives the shock, instead of pushing it as indicated on 

 Plate XXXIY. To effect this (the contrivance cannot be very clearly described with- 

 out the aid of further drawiags) the end of the percussion timber, jp, nearest the cam is 

 furnished with two stout iron plates, one attached to each side of the timber and 

 extending toward the cam ; the two plates are connected at their other ends by a cast- 

 iron piece which fills the space between them, and the inner stu-face of which is curved 

 so as to correspond to the curve of the cam. The latter revolves between the two 

 plates, in the reverse direction from that indicated in Fig. 1, and, striking against the 

 cast-iron piece, draws the table to one side. When the table is released by the cam it 

 is drawn to the opposite side by the action of a spring, which, as in the case already 

 described, is of wood,* but is placed horizontally, the two ends being fixed and the mid- 

 dle attached to the end of the percussion timber. When thus drawn forward the end 

 of the percussion timber strikes against a buffer, which is firmly secured in an iron bed- 

 plate that is screwed down to an tmderlying timber; and as the sharjjness of the shock — 

 an important condition for effective work — depends upon the firm position of this tim- 

 ber, the latter is made long enough to extend entirely under the table to the opposite 

 side, and is fixed by holding-down bolts to a solid foundation of masonry. The timber 

 is connected with and braced by other timbers that are so laid in the masonry as to dis- 

 tribute the shock as evenly as possible to the entire mass of the latter. The opposite 

 end of the timber may serve as the foundation for the supports of the cam-shaft, one 

 end of which is furnished with a driving-pulley and the other end with a 400-pound to 

 600-pound fly-wheel, 3 feet in diameter. 



The movement of the table is guided by two uprights, one on each side of the per- 

 cussion timber. 



The buffer is adjustable, and by advancing or retiring it, the length of the stroke 

 may be regulated. 



