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All those who exhibited American mining machinery at the Melbourne Exhibition state emphatically that no quartz-mill owner or battery-manager in America would ever think of putting large pieces of quartz into a stamp-mill. All the material which will not pass over a grizzly is put through rock-breakers, and reduced to a maximum size of about 2in. in diameter. The ore as it leaves the mine is conveyed in trucks and dumped on to a grizzly, and what will not pass through runs down over the grizzly into the stone-breaker. The ore-bins or paddocks are generally" sufficiently large to admit of holding all the quartz or ore that can be raised from the mine in one shift. The paddocks also should be at such an elevation above the reduction machinery as will admit of the material being all led down through the different processes by gravitation. Bock-breakers are the most important adjuncts in connection with crushing ores, and are the cheapest form of crusher which has yet been brought into general use. Indeed, they do a large portion of the work, and bring down the ore to a somewhat uniform size, that admits of far more work being done by stamps. When large pieces of hard-quartz ore are fed into the stamps the first blow breaks certain large portions, sending them at a high velocity against the screens, which tends to burst them, or, at least, to knock holes in them; whereas if the material is well broken before going into the stamping-mortar this does not take place to the same extent. Also, when the material is of a uniform size it can be fed into the stamping-mortar with much more regularity; and on this depends in a great measure the quantity of ore that can be pounded up sufficiently fine by the stamps to pass through the grating or screen. All the ore coming from the bins or paddock should be run into an ore-feeder, which feeds the stamps automatically, and these ore-feeders can be so nicely adjusted that there is always a uniform quantity of loose material in the stamp-mortar; the great desideratum being to get the stamp to do the maximum amount of duty, provided that a maximum percentage of the value of the ore shall be the result. The regularity of feeding is deserving of study and attention. It depends to a certain extent on the class of ore that is being crushed : if it is low-grade, containing sulphurets, it may be found more economical not to have too fine a screen, and to keep the stamp as close down to the die as possible. The less the quantity of material—that is, within certain limits—which lies between the die and stamp, the greater the quantity will be put through. But this is a matter which a batterymanager can best determine, so as to get the best results in working the different classes of ore. In mentioning the descriptions of stamping-mortars, Joshua Hendy, of the City Ironworks, San Francisco, states, " They are made of different forms, to suit the peculiarities of the gold- and silverbearing ores, as well as their value. They are made for low, high, and overflow discharge, sometimes wide and flaring, sometimes narrow and contracted at the bottom up to the discharge-opening. The conditions of use must determine the form to be adopted. For gold-mills the discharge lip or apron should be of iron, cast as part of the mortar, as this prevents any leakage escaping from around the screen-frame. This lip or apron should be gradually drawn or tapered to the point of discharge, which should be open and not less than 16in, wide—the width of the discharge-sluices— and an easy descending grade be given, to permit of an even and shallow flow of the pulp over the copper or silver plates with which the bottoms of the tables are covered. The frames of the sluices should never be constructed in contact with the mortars or battery-frames, but independent, and resting upon independent bearings, so as to prevent jar and thereby leakage The screen-frames should be set with an outward inclination at the tops, and for milling gold-ores of an average value the distance from the bottom of the screens as set in the frames to the top of the dies in the mortars should be at least 7in." The whole pith of this is that, the screens being so high above the top of the dies, there is far less wear and tear on the screens, and, the discharge being high, fine crushing can be accomplished with a much coarser grating than would be required were it set down to within 2in. of the top of the dies, as is done in many cases in the colonies. There is no gainsaying the fact that we can learn a great deal from the Americans in the matter of reducing and pulverising ores, and also with respect to their subsequent treatment. The defects in the stamping-batteries in use in the Australasian Colonies are as follows :— (1.) The cam-shaft is placed too far away from the stamp-shank. (2.) The cams in many batteries are not properly curved. (3.) The stamp-mortar is too wide for the diameter of the stamp-shoe used, and the stamps are placed too wide apart in the mortar. (4.) The screens or grating are not properly set to produce a maximum discharge. Position of the Gam-shaft. —There is scarcely a stamping-battery constructed in the colonies where the cam-shaft is less than 2in. distant from the stamp-shank, and there are many where the distance is over 3in. The result of this is they require more power to drive them, and they cannot be run at a high speed. This will be seen by any one after a few moments' reflection. Say, for illustration, that the diameter of the cam-shaft is 4-J-in., and of the stamp-shank 3in., the distance from centre to centre if the two were close together would be 3f in.; but, as it requires a clearing between them, so that in vibration the surfaces of the shaft and stamp-shank will not touch one another, of say, -jin., then the fulcrum would be 4in. If a clearing of 3in. is left between the two, then the fulcrum becomes 6fin., instead of 4in., which is ample to do the work. The difference in the power, therefore, required to lift the stamp on a fulcrum of 6fin. beyond that required on a fulcrum of 4in. is in exact proportion to its length. If a lever 4ft. long had a fulcrum of 6fin., and 8001b. were placed on the fulcrum end, it would require 112-|lb. on the end of the lever to balance it; but if the same lever had a fulcrum of only 4in. it would require 66-flb. to balance it. The same thing applies in relation to the lifting of the stamp: the power applied is then as follows: As 112-5: 6666: : the weight lifted: to the difference or saving in the power required to do the work. This clearly demonstrates that there is a 'great waste of power used in working our stampingbatteries. The saving in power if the batteries were properly constructed would soon pay for a