670 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1913. 



size, shaj3e, and surface of the opposing electrodes; but it is found 

 in practice that the negative discharge is much the more stable and 

 can be run at higher current without danger of disiniptive discharge, 

 so that it has now become standard practice to make the discharge 

 electrodes the negative and the grounded collection electrodes the 

 positive.^ In order to help maintain the charge on the electrode in 

 the interval between these contacts, the Ley den jar (I) seen in the 

 picture was connected in parallel with the electrodes. The wire lead- 

 ing to the jar walls or collecting electrode was usuall,y grounded for 

 convenience and safety, as, in fact, has been done throughout all the 

 practical installations. This leaves but one high-potential conductor 

 to deal with in each precipitation chamber and greatly increases the 

 safety of operation. 



Figure 4 is a closer view of the precipitation chamber through 

 which the acid fume is being blown at the rate of about 20 liters per 

 minute, the electric current being shut off of the apparatus. Figure 

 5 shows the effect of turning on the electric current with the same gas 

 steam still flowing. 



The discharge electrode in this case consisted of a cylinder of wire 

 screen (C), wrapped with a few turns of asbestos sewing twine (c) 

 and suspended by a wire passing through a glass tube as shown. The 

 suspended particles of acid were driven away from the asbestos fila- 

 ments and deposited on the walls of the bell jar, finally running down 

 into the U tube below. 



The next undertaking was to duplicate these expermients on a scale 

 some two hundred- fold larger. This was carried out during the same 

 summer at the Hercules works of the E. I. du Pont de Nemours Pow- 

 der Co. at Pinole, on San Francisco Baj', where the contact gases 

 from one of their Mannheim contact sulphuric acid units were em- 

 ployed. 



Figures 6 and 7 are photographs taken about a minute apart with 

 The same current of fume-laden gases passing into the precipitation 

 chamber, but with the electric current respectively off and on. The 

 apparatus Avas the same in general principle as the small laboratory 

 unit described above. The precipitated acid drained off from this 

 ])recipitation chamber into the carboy on the right. Current Avas 

 supplied from three 1-kilowatt 110-volt to 2,200-volt transformers 

 connected in series on their 2,200 volt side to give 6,600 volts. In this 

 apparatus the power consumption was about one-fifth of a kilowatt, 

 and between 100 and 200 cubic feet of ^as per minute could readily 

 be treated. 



1 The Positive and Negative Corona and Electrical Precipitation, W. W. Strong. Trans. 

 Amer. I^st. Elect. Eug., vol. ^2, pp. 1305-1314, Cooperstown meeting, June 27, 1913. 

 Also U. S. Pat. 1067974, Cottrell, .Tul.v i.'2, 1913. 



