620 MINING INDUSTRY. 



crushing and concentrating machinery, by which means the valuable mineral 

 is separated from the worthless gangue and prepared for smelting ; and fur- 

 naces, the object of which is, as at present contemplated, to save not only 

 the silver, but also the lead. During the years 1867 and 1868 some experi- 

 mental works were erected, containing a number of Scotch hearths, which 

 were used to produce pigs of argentiferous lead, in which form the valuable 

 products of the ore were shipped east for separation. It soon appeared, . 

 however, that a larger proportion of the ore, than had at first been supposed, 

 existed in forms poorly adapted to this method of treatment, and the Scotch 

 hearths were therefore abandoned, with the view of erecting furnaces capa- 

 ble of treating the several varieties of lead, zinc, and copper ores that are 

 found in the vein. The construction of these furnaces, at the time of the 

 writer's visit, had just been commenced. The processes to be employed 

 closely resemble those in use at Pont-Gribaud, in France, and Freiberg, in 

 Saxony. They involve the roasting of the dressed mineral, and their subse- 

 quent smelting, in such manner as to obtain pigs of lead in which all the 

 silver should be contained. These pigs, thus obtained, will be shipped to 

 Newark, where the separation of the metals may be effected. It is esti- 

 mated, by Mr. Collom, the manager, that the value of the lead alone will pay 

 the expenses of working, leaving the silver as a profit. As the furnaces were 

 not constructed at the time referred to, a detailed description of the pro- 

 posed processes is omitted here. They are given at length in several metal- 

 lurgical treatises. 



The concentrating machinery, used for the preliminary dressing of the 

 ore, as a preparation for smelting, comprises two Dodge crushers, a series oi 

 Cornish rollers, screens or appliances for sizing the material, and four of Col- 

 lom's ore-washing machines. The last-named apparatus has been proved by 

 long experience, not only in the district referred to in these pages, but else- 

 where in our mining regions, as a most useful and efficient ore dresser. As 

 it is believed to be a machine that may be advantageously introduced into 

 some of our western mining districts in which concentration is yet to become 

 an important feature in the manipulation of ores, a brief description of it is 

 given here. 



The drawings on Plate XXXVII show some of the details of the con- 



