666 ANNUAL EEPORT SMITHSONIAN INSTITUTION, 1913. 



veloping them into commercial realities. The subsequent work may 

 fairly be considered as the reduction to engineering practice as re- 

 gards equipment and construction of the fundamental processes long 

 since laid open to us by the splendid pioneer work of Lodge, a feat 

 vastly easier to-day than at the time of Lodge and Walker's original 

 attempt. 



THEORY OF P^LECTRICAI. PRECIPITATION. 



The precipitation of suspended matter, whether in gases or liquids, 

 may be accelerated by electricity in the form of either direct or 

 alternating current, but the mode of action and the type of problem 

 to which each is best applicable differ in certain important respects. 



Where an alternating electromotive force is applied to a suspen- 

 sion the action consists for the most part in an agglomeration of the 

 suspended particles into larger aggregates out in the body of the sus- 

 pending medium and a consequently more rapid settling of these 

 aggregates under the influence of gravity. 



Thus, it has been stated that if powerful Hertzian waves are sent 

 out under proper conditions into foggy air the alternating fields set 

 up in space cause an agglomeration of the particles of liquid into 

 larger drops, which then settle much more rapidly. Considerable 

 work aimed at the application of these phenomena to the dispelling 

 of fog on land and sea was said to have been done some years ago in 

 France and England, but very little as to definite results appears to 

 have been published. Another application of alternating current 

 along these lines is found in a process now in use in the California oil 

 fields for separating emulsified water from crude oil.^ 



Alternating current may thus be used to advantage where the 

 masses of fluid to be treated are fairl}'^ quiescent, and a simple 

 agglomeration of the suspended particles into larger aggregates is 

 sufficient to effect separation by gravity or otherwise. 



In the case of the large volumes of rapidly moving gases in smelter 

 flues the agglomerating and settling process is, however, too slow 

 even when the flues are expanded into as large dust chambers as are 

 commercially feasible. It is in such cases that unidirectional current 

 methods have been particularly unportant. 



If we bring a needle point connected to one side of a high poten- 

 tial direct-current line opposite to a flat plate comiected to the other 

 side of the line we find that the air space between becomes highly 

 charged with electricity of the same sign as the needle point, irre- 

 spective of whether this is positive or negative, and any insulated 

 body brought into this space instantly receives a charge of the same 

 sign. If this body is free to move, as in the case of a floating particle, 



1 See " Dehydration of Crude Petroleum, a New Electrical Process," Arthur T. Beazley, 

 The Oil Age (Los Angeles), voU 3, pp. 2-4, Apr. 21, 1911. 



