EXPERIMENT STATION BULLETINS. 



579 



dislodged from their original position in reference to each other and the 

 sides of the glass container. 



Platinized electrodes were used in all the tests and the platinizing was 

 according to the usual method (5). When the electrodes receive a coat 

 of platinum black their surfaces are immensely increased and polarization 

 is negligible. Tlie electrodes were frequently cleaned and replatinized. 

 Dr. Clark of the University of Illinois has suggested that the cleaning 

 process can be greatly facilitated by placing the electrodes in Aqua Regia 

 with a reversal of the current every minute. It takes only a few minutes 

 to clean them thoroughly. AVhen not in use the electrodes are kept in 



Fig. 13. 



Resistance Cells. 



Explanation of different types in text. 



conductivity water (about 2.0x10-6), Before using the cells, they are 

 tested for constancy and when two successive readings of conductivity 

 water give the same figures, the cells are considered in proper condition 

 to use. 



The various forms are shown in Fig. 13, Nos. 1, 4 and 5 are for solutions 

 of low conductivity and Nos. 3 and 6 for high conductivity and No. 2 for 

 medium conductivity. Nos. 4 and 5 are the plunger types to be used to 

 determine the resistance of solutions in any size or form of beaker. This 

 type eliminates the side effects. No. 7 is used when it is desired to meas- 

 ure the resistance of living tissues. Discs of the living tissues are pre- 



