SMOKE AND DUST ABATEMENT COTTRELL. 669 



are to-day the chief stumbling block of the power companies in going- 

 very far above 100,000 volts on these lines, become exactly what is 

 desired in the processes of precipitation, and with the voltages now 

 used a bare metal w^re of moderate size or the relatively thin edge of 

 a metallic sheet may be made to furnish an excellent discharge. 



The construction and arrangement of the electrodes, as also of the 

 chamber containing them, naturally varies very widely with the con- 

 ditions to be fulfilled under the varied applications to which the 

 process may be put. Some of the more general features of this work 

 are described in patents^ already issued in this and foreign coun- 

 tries, while further details and modifications are covered in other 

 patents not yet issued from the various patent offices. The accom- 

 panying photographs give perliaps a better idea of the gradual de- 

 velopment of the work than any detailed description which would be 

 possible in the space here at command. 



LABORATORY EXPERIMENTS. 



Figure 3 is the apparatus used for the original laboratory experi- 

 ments in the spring of 1906. Sulphuric-acid mist was generated by 

 bubbling the gas from the little contact sulphuric-acid plant, seen 

 on the table, through water in the U tube beneath the inverted glass 

 bell jar (A),'- whose inner walls were quickly wetted sufficiently with 

 acid to act as the collecting electrode, a wire being inserted along- 

 side of the stopper through which the U-tube connected with the bell 

 jar and served to connect the jar walls to the induction coil, on the 

 left, the latter acting as the step-up transformer (O). This coil re- 

 ceived alternating current at 110 volts from the lighting circuit and 

 gave about 3,700. volts at its secondary. The other high potential 

 terminal of the induction coil was connected to the discharge elec- 

 trode (C) within the bell jar through a make and break (M J N), 

 operated by the synchronous motor (L). This latter was improvised 

 by substituting a plain iron cross for the squirrel-cage armature in an 

 ordinary fan motor operated from the same 110- volt line as the 

 induction coil and brought into step by the induction motor on the 

 right. A momentary contact with the discharge electrode was thus 

 established once each complete cycle at the peak of the voltage wave 

 and served to charge this electrode to the maximum voltage of the 

 line, always with the same polarity. As stated above, electrical pre- 

 cipitation takes place no matter whether the discharge electrode is 

 made the positive or negative, and the direction of the discharge and 

 deposit is independent of the polarity and determined only by the 



lU. S. Pats. 866843, 895729, 945917, 1016476, 10.35422, and 1067974. The second of 

 these also practically reprinted by Ens;. Min. .Touru., vol. 86, pp. 375-377 (1908j, 

 Germ. Pats. 258435, 265964, and 270757, and corresponding patents in various other 

 countries. See also in this connection German Pats. 208740, 230570, and 238958. 



= The letters in parentheses refer to corresponding parts in the diagram (fig. 2). 



