218 MINING INDUSTEY. 



economy of power; to obtain the most favorable conditions for amalgamation, 

 depending mainly on the free circulation of the pulp, the uniform and 

 thorough distribution of the quicksilver, and the proper degree of heat; and 

 to combine, with these requirements, simplicity and cheapness in construction, 

 facility in management and repair, large capacity, and economy of time, labor, 

 and materials in the performance of duty. 



The attempts that have been made to obtain these results have met with 

 varied success, the different devices of any one pan sometimes obtaining a 

 high degree of excellence in certain details at the cost of it in others. 



Among the diiferences in characteristic features of pans the most notice- 

 able is that of the bottom and the grinding surfaces, some being flat, and 

 others variously curved; other details, of more or less importance, such as the 

 construction of the muUer and the method of attaching it to the driver, the 

 form of the shoes and dies, the means of fixing them in place, of providing 

 for the heating of the pulp and for its circulation during the grinding and 

 amalgamating process, vary considerably in the several patterns. 



The opinions of practical mill-men are somewhat divided regarding the 

 comparative advantages of the different forms of pan-bottoms. The prevail- 

 ing opinion, however, among those with whom the writer has conversed, 

 seems to be, all things considered, in favor of the flat bottom. While other 

 forms of grinding surfaces may possess superior advantages, theoretically, their 

 greater efficiency, in practice, is often lost by the unequal wear of the surface 

 of the muUer, usually resulting from the difficulty of keeping the other parts 

 of the machine, on which the grinding surfaces depend, in perfect order. 

 The various parts of the flat muUer are simpler in form, more easily handled, 

 and more conveniently replaced when worn out. While the flat-bottomed- 

 muUer involves the expenditure of more power in carrying its load of thick 

 pulp, this disadvantage is counterbalanced, in the opinion of some, by the 

 more complete distribution of the quicksilver and the, consequently, more 

 perfect amalgamation. 



The flat-bottomed pans of Varney and of Wheeler, and that of Hepburn 

 and Peterson with conical bottom, have been widely used during several years 

 past. Some improvements have been added to them lately, and they are stiU 

 held in high esteem by mill-men. Within the last year or two, other makers 



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