680 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1913. 



Another installation to treat about 100,000 cubic feet of gas per 

 minute and consisting of 384 pipes, each 13 inches in diameter, is 

 also under construction at the lead smelter of the Consolidated Min- 

 ing & Smelting Co. at Trail, British Columbia. 



Another unit of tubular type is seen in figure 37. In this case the 

 pipes are of lead 12 inches in diameter and 12 feet long. This unit 

 was constructed at Anaconda to collect the copper and acids vola- 

 tilized from an 80-ton experimental MacDougall furnace, roasting 

 low-gi-ade sulphide tailings with salt preparatory to leaching.^ Fig- 

 ures 38 and 39 are the same, with the electric circuit of some 60,000 

 volts, respectively, off and on. 



Where the material collected is largely liquid or saturated with 

 acid, as in this case, both wood stave and vitrified terra-cotta pipes 

 up to 2 feet in diameter have also been used with success, and with 

 dry material iron-pipe construction has been successfully employed 

 up to 36 inches diameter and 20 feet in length. In these larger pipes 

 several discharge electrodes are sometimes employed, carried on a 

 central support. 



This type of construction, where applicable, has done much to sim- 

 plify and reduce cost of installation. 



ELECTRICAL PRECIPITATION AND GASEOUS CONSTITUENTS. 



The electrical process, it must be remembered, precipitates only sus- 

 pended particles, be they liquid or solid, but does not in itself extract 

 any of the truly gaseous constituents of the mixture under treatment, 

 Wliat is gas under one set of conditions may, however, be solid or 

 liquid under others. Thus recent experiments upon arsenic-refining 

 furnaces at Anaconda have indicated the practicability of installing 

 two precipitating units in series, the first treating the hot gases as 

 they come directly from the furnaces roasting crude flue dust, their 

 temperature at this point being so high that the arsenic is for the 

 most part in the form of true gas, and onlj!^ the nonvolatile dust me- 

 chanically carried over by the draft is precipitated. Beyond this 

 unit the gases are cooled by admixture of cold air, and the arsenic 

 separates as a cloud of solid fume, which is then precipitated in a 

 state of high purity in the second electrical precipitation. 



This principle might, of course, also be applied in a greater num- 

 ber of stages to mixtures of materials of different volatilities and 

 in this way opens up new possibilities for the application of frac- 

 tional distillation and condensation. 



Another indirect method of removing a particular gaseous con- 

 stituent from a mixture by the electrical processes is illustrated by 



1 " Roasting and Leaching Tailings at Anaconda, Mont.," by Frederick Laist, Bull. 

 Amer. Inst. Mln. Eng., vol 70, pp. 1147-1162, July, 1913. 



