DEPARTMENT OF METALLURGY AND ECONOMIC GEOLOGY. 157 



A full series of chromium ores, presented by the Tyson Manufacturing 

 Company, Baltimore, Maryland. 



A full series illustrating the smelting of iron at the Pennsylvania 

 furnaces of Eobert Hare Powels' Sons & Co., Philadelphia, Pennsylvania. 



A complete and very valuable collection illustrating the smelting of 

 silver-lead or base bullion at the Colorado Smelter, South Pueblo, Col- 

 orado, presented by Mr. Anton Eilers, South Pueblo, Colorado. 



This last collection is exceedingly full and complete, and is accompa- 

 nied by a description of the process, with diagrams and many analyses, 

 which render it especially valuable. It well illustrates the kind of col- 

 lections that it is desirable for the department to gather in order to com- 

 plete the systematic series. 



The ores as received at the works are classified into oxidized and sul- 

 phureted ; the oxidized ores are further divided into basic and silicious, 

 that is, basic ores, the gangue of which is essentially a base, and silicious 

 ores, the gangue of which is essentially acid or silica ; these are sent di- 

 rectly to the shaft furnaces. The sulphureted ores are also divided into 

 basic and silicious. In this case, however, it is the ores that are high 

 in sulphur that are called basic, for the reason on roasting they furnish 

 mainly oxides, which act as bases in the smelting operation. The sili- 

 cious sulphureted ores consist essentially of quartz, with only a small 

 amount of sulphides ; they are generally very rich in silver and poor in 

 lead, being more nearly true silver ores. 



The basic sulphureted ores are separated into coarse and fine. The 

 coarse are roasted in stalls and then go to the shaft furnaces ; the fine 

 are roasted in reverberatory furnaces, and are sometimes fused at the 

 end of the roasting and sometimes not. From the roasting furnaces 

 they go directly to the shaft furnaces. 



The silicious sulphureted ores are sometimes roasted in the fusion 

 furnace, but they are generally sent to the shaft furnaces, especially 

 when they are very rich in silver. 



The fluxes are all basic, and consist of iron ores and limestone, and 

 go direct to the shaft furnaces. 



The products of the smelting in the blast furnaces are: 



Base Bullion, the valuable product which goes to market. 



Slag, containing the earthy constituents of the furnace charge — 

 divided into clean, or free from lead and silver, which is thrown over 

 the dump; and impure, that is, containing lead and silver, which goes 

 back to the shaft furnaces. 



Matte, a by-product, essentially a sulphide of iron and copper, which 

 goes to the roasting stalls and then back to the shaft furnaces. 



Speiss, a by-product, essentially an arsenide of iron, which goes to 

 the roasting stalls and then back to the shaft furnaces. 



Flue dust, deposited in the flues of the furnaces, which is mixed with 

 lime and ores low in lead, roasted in the fusion furnace, and then goes 

 back to the shaft furnaces. 



