were restricted to metals and materials of generally low cost and ready 

 availability on the market. 



The electrode tests were conducted in a concrete tank equipped 

 with an insulating liner. The particular two electrodes used in any one 

 test were suspended vertically into the center of a 37-inch-wide x 17-foot- 

 long tank which was filled to a depth of 23 inches with water pumped 

 from Lake Huron. The spacing between round electrode axes was held con- 

 stant at ij. feet. All round electrodes tested were suspended in a verti- 

 cal plane passing through the long axis of the tank and immersed to a 

 depth of 12 inches. Flat electrodes (6-l/U inches wide) were hung from 

 the same suspensions but in two parallel planes spaced U feet apart and 

 both perpendicular to the long axis of the tankj they likewise were im- 

 mersed to a depth of 12 inches. 



The voltage gradient probe described earlier in this section 

 was suspended midway between the electrodes so that its terminals lay 

 6 inches beneath the water surface at the intersection of a vertical 

 plane passing through the long axis of the round electrodes, the vertical 

 center lines of flat electrodes, and a horizontal plane parallel to the 

 surface. 



A variable transformer, powered by a 110 volt AC line, was used 

 to control the output voltage of a 1 : 1 ratio isolation transformer. 

 The secondary or output voltage of this transformer was fed into the two 

 electrodes under test and was held constant at 5>0. The voltage gradient 

 as measured across the terminals of the probe in a particular test was 

 used as the criterion of the effectiveness of the electrodes used. 



29 



