OKLAHOMA ACADEMY OF SCIENCE 137 



while the other passes through the cell and is made use of as a 

 pulsating unidirectional current. With four cells it is possible 

 to rectify both alternations thus making the capacity twice as 

 great. In this form, as shown in figure 1, it was placed on the 

 market by a Paris firm in 1504. In practically the same form the 

 Nodon Valve was manufactured and placed on the market in this 

 country two or three years later. While it has not proved to be 

 what some of its early supporters claimed for it there is neverthe- 

 less a distinct advantage in its use where more expensive devices 

 cannot be had. 



It is possible to get as much as eight or ten amperes at fifty or 

 sixty volts but that strength of current cannot be maintained for an 

 indefinite period without some method of cooling. In ten or fifteen 

 minutes the ordinary cell will not heat sufficiently to cut doAvn its 

 efficiency materially but in an hour it probably will do so. On 

 small currents not exceeding an ampere or two it is not necessary 

 to give it any attention even though the rectifier is in continuous 

 use for two or three hours. Fortunately it is seldom that a heavy 

 current is wanted for a very considerable length of time. 



One of the reasons for the lowering of the efficiency due to 

 the rise of temperature is that at the higher temperatures the so- 

 called film on the aluminum plate tends to break down. The theory 

 is that when the aluminum plate is made the anode electrolysis is 

 set up which tends to cover the aluminum plate with a film con- 

 sisting m.ain'y of aluminum oxide. The length of time needed to 

 build this film, depends upon current-intensit}^ If only a sm.all 

 fraction of an ampere is used it will require from forty-five min- 

 utes to an hour ; with eight or ten amperes the film appears almost 

 instantaneously, the voltage across the cell rising as has just been 

 mentioned, to eighty in three seconds. In a few minutes the voltage 

 reaches a maximum and the so-called film is completed. The 

 theory offered by Nodon, and later up-held by Burgess and Ham- 

 beuchen of Wisconsm, is that the so-cal'!ed stoppage is due to an 

 ohmic resistance offered by the film. Wilson measured the resist- 

 ance of the cell and reported it something like 10,000 ohms. The 

 writer made several measurements and obtained values ranging 

 from 7000 to HOG ohms depending upon temperature of electro- 

 lyte and general conditions of the cell. Guthe, Taylor and Inglis, 

 and Cook offered different theories. Cook's theory is worthy of 

 special mention. He held that the resistance of the cell was due to 

 a counter-e!ectromotive force set up by the highly charged anions 

 collecting about the anode and not being allowed to discharge on 

 account of the non-conductivity of the film. This seems a more 



