662 ANNUAL REPORT SMITHSONIAN INSTITUTION, 191.'}. 



higher content of acids and are much used in lead ymelting and in 

 some copper smelters, but even their limit is soon reached, and in 

 the majority of copper-smelting plants their use has been considered 

 impractical unless the gases are first neutralized by additions of basic 

 oxides, such as those of calcium or zinc. The resistance to the 

 passage of the gases through the fabric, especially after the solids 

 begin to collect in the pores, is also a serious item in large scale 

 operation, as the fan power required to maintain the draft is often 

 very large. 



The use of fine wire screen and of asbestos in place of cotton or 

 woolen fabrics has been repeatedly suggested and extensive experi- 

 ments have been made with such materials at different plants, but 

 they have not proved generally serviceable, due chiefly to their high 

 cost and the clogging of the pores, rapid corrosion of the wire when 

 fine enough to filter effectively, and the tendency of asbestos to be- 

 come brittle in highly acid atmospheres. 



Besides the bag filters, much less has been made of chambers or 

 towers filled with coke, gravel, sand, sawdust, slag wool, and even 

 asbestos fiber, but for large volumes of gases, especially when they 

 carry a considerable weight of solids, such filter structures if made 

 tight enough to be effective, introduce an enormous resistance and 

 consume a corresponding amount of power, to say nothing of the 

 labor of cleaning, so that their practical use may be considered as 

 confined to rather special cases and relatively small gas volumes. 



SETTLING CHAMBERS AND BAFFLES. 



Even the interposition of large flues or chambers in the course of 

 the gases on their way to the stack by temporarily decreasing their 

 velocity greatly aids in settling suspended matters and form a part of 

 almost every metallurgical flue system. If baffles in the form of plates 

 or wires are hung in these chambers, their efficiency as dust settlers 

 is greatly increased, but, of course, at the expense of draft, which 

 must usually be compensated for by additional height of stack or fan 

 power. These chambers are, of course, relatively much more effective 

 as settlers for coarse than for fine particles, and it is impractical by 

 their use alone to effectively eliminate real " fume "' or smoke. Prob- 

 ably the largest and best illustration of this system is at the Ana- 

 conda Copper Mining Co.'s smelter at Great Falls, Mont.^ A few 

 years ago this plant installed in its flue system a chamber 177 feet 

 wide, 367 feet long, and 21 feet deep, with iron wires hung from 

 top to bottom, spaced about 2 inches apart, each way throughout the 

 chamber, making the aggregate length of wire some 4,000 miles, or 

 about equal to the earth's radius. To overcome the resistance to draft 



1 " The Great Falls Flue System and Chimney," by C. W. Goodale and J. IT. Klepinger, 

 Bulletin American Institute of Mining Engineers, August, 1913, No. 80, pp. 1935-2010. 



