TEEATMENT OF THE COMSTOCK OEES. 211 



stamp and head are tbeii allowed to drop upon it. If necessary, a few blows 

 of the hammer must be struck upon the top of the stamp-stem. The whole 

 may then be raised, the shoe keeping its place, and suffered to fall repeatedly 

 until the shoe is firmly established in the socket. During this operation a 

 piece of plank is interposed between the die on the bottom of the mortar and 

 the shoe for the latter to strike upon. Whenever a shoe has been worn out 

 it may be removed from the socket by driving the key into the key-way, c, 

 and forcing it off. Care is required that the shoe does not become so thin as 

 to permit the head to sustain undue wear and so become weakened. Shoes 

 should be removed when worn down to one inch of thickness. 



The collar, or tappet, is a projecting piece, firmly secured to the upper 

 part of the stem, by means of which the revolving cam may lift the stamp 

 and let it fall upon the substance to be crushed. Tappets vary in form and 

 method of attachment to the stem, but that which seems to combine the 

 greatest number of advantages and to have been most generally adopted in 

 Cahfornia and Nevada is that which is known as Wheeler's gib-tappet. Fig. 

 4, on Plate XX, shows an elevation and vertical section of this contrivance. 

 It is a piece of cast iron, cylindrical in form, about 8 inches in height and 

 diameter, hollow at the center so as to receive the stamp-stem. To secure 

 the tappet to the stem there is a gib, g, about 2 inches wide and nearly as 

 long as the tappet, having its inside face curved so as to correspond in form 

 to the circular hole through which the stem passes. The gib being fixed in 

 its place in the tappet and the latter being put upon the stem, it is pressed 

 against the stem by means of two keys, k, k, driven into the key- ways, with 

 force sufficient to hold the tappet and stem firmly together and prevent slip- 

 ping between them. This is found to be a very effective method of securing 

 the tappet while permitting it to be fixed at any desired point on the stem, 

 according to the wear of the shoe. The stem is uniform in size and the work 

 of cutting facings, screw-threads, and key-seats on the stem, required by 

 other methods in use elsewhere, is thus avoided. 



The rotary motion of the stamp, imparted by the friction of the cam 

 against the tappet, is in very general use in Nevada. This is one of the ad- 

 vantages offered by the use of round shoes, stems, and tappets. The revolv- 

 ing cam, meeting the tappet, and raising the stamp, causes it while being 



