208 MINHSTG INDUSTEY. 



former case there is often great difficulty in keeping the mortar tight enough 

 to prevent leakage and consequent waste of ore. 



The mortar in general use for wet-crushing is an iron box or trough 

 about 4 or 5 feet in length and depth, and 12 inches, inside, in width, and so 

 cast that bottom, sides, and ends are in one piece. A front and end view of 

 one of the most-approved forms is shown in place, in the drawing of a bat- 

 tery of stamps, on Plate XIX. The feed opening, /, is an aperture about 3 

 or 4 inches wide and nearly as long as the mortar, by means of which the 

 rock is supplied to the stamps. On the opposite side is the discharge open- 

 ing, furnished with a screen, i, through which the crushed material must 

 pass. This opening is as long as the mortar, or nearly so, and 12 to 18 inches 

 deep, the lower edge being 2 or 3 inches above the top of the die. In some 

 mortars, especially for dry crushing, the discharge is on both sides, in which 

 case the feed-opening is above the screen ; but the single discharge is in gen- 

 eral use in the Washoe district. 



The screen is attached to a screen frame, j, which is secured in grooves 

 cast in each end of the mortar, and by two lugs, o, cast in front of the dis- 

 charge-opening, being held firmly in place by a wedge driven behind it in the 

 grooves just referred to. 



Screens are sometimes placed vertically, sometimes inclined, as shown 

 in the figure. The discharge is generally thought to be better in the latter 

 case. Screens are made of fine brass wire-cloth, having from 40 to 60 meshes 

 to the hneal inch, or, more generally for wet-crushing, of Eussia sheet-iron, 

 perforated by finely punched holes, varying from Jg- to -^ of an inch in diam- 

 eter. The wire-cloth or sheet-iron plate is attached to the screen-frame by 

 nails or screws. The punched plate is preferred for wet crushing. The wire- 

 cloth, though afibrding more discharging surface, wears out faster, and not 

 only is more liable to break, and so permit large particles to pass through, but 

 frequently stretches, giving meshes of irregular size. A piece of canvas is 

 usually hung before the screen for the crushed ore to splash against as it 

 issues from the mortar, falling thence into the trough below. 



Dies. — The mortar is furnished with dies which are so fixed in the bot- 

 tom as to receive the blow of the stamp and sustain the wear which would, 

 in its absence, fall upon the mortar itself The die is a cylindrical piece of 



