578 



STATE BOARD OF AGRICULTURE. 



balance out the capacity in the electrolytic cup. This condenser must be 

 chosen with a view to avoiding any leakage and therefore its insulation 

 must be sufficiently high. An error of .2 of 1% is apt to occur from this 

 cause. In making a measurement, take as much care to balance the 

 capacities as you do to balance the resistances. 



ELECTROLYTIC CELLS. 



The cells used in these experiments were of different forms depending 

 upon the purpose for which they were to be used. The materials from 



Fig. 12. 



1. Resistance box. 



2. Condenser. 



Curtis Coils. 



which they were made were Jena glass, hard vulcanite rubber, and plati- 

 num. Jena glass was chosen because it is one of the least soluble of all 

 makes of glass. The slightest impurity from the glass or air causes an 

 error in the resistance of the solution. The glassware was thoroughly 

 cleaned by soaking it in a hot solution of potassium dichromate in sul- 

 phuric acid and afterwards rinsed in distilled water. The final treatment 

 consisted in a steaming process for a few hours. "Conductivity water" 

 showed no change in resistance after staying in cups prepared as above 

 for a period of at least twenty-four hours. The hard vulcanite rubber 

 parts were kept clean. The platinum was at least .85 mm. thick and 

 rigidly fused to the glass connections. Tliis prevented any change in 

 the cell constant which would happen if the electrodes were in any way 



