H. E. Bobbins — Conductivity Cell for Electro-titration. 249 



Art. XI Y. — Conductivity Cell for Electro-titration • by 

 Harold E. Robbies. 



The type of cell shown in the accompanying sketch (p. 250) 

 was devised with the following requirements in view : (a) pro- 

 tected electrodes : (b) unobstructed access to electrolyte with 

 burette ; (c) adequate mixing of the electrolyte without the com- 

 plications of mechanical stirrers ; (d) sufficient rigidity to 

 permit of frequent cleaning and handling, combined with 

 economy of materials. 



It will be seen that these requirements are met when each 

 item is considered in detail, (a) The electrode holder, C, has 

 an outer shell which projects beyond electrodes and protects 

 them from accidental injury, while leaving them readily 

 accessible. The platinum foil electrodes are themselves curved 

 for rigidity and sealed into the glass mercury tubes with No. 

 20 platinum wire, The mercury tubes are sealed at the top to 

 the wall of the surrounding glass protector. 



(b) The space between the mercury tubes and the shell is 

 sufficient to permit the ready introduction of reagents from 

 burettes. 



(c) The mixing is performed as follows : The electrode 

 holder, C, fits loosely into the cell jar, B, the base of the 

 holder resting on base of B. Attached to S is a soda-lime 

 tube and mouth-piece. When the cell is placed in thermostat, 

 and some reagent is added to solution in the cell, suction on 

 mouth-piece causes the electrolyte to rise into M. The elec- 

 trolyte is then allowed to run into B and the operation is 

 repeated. Repeated tests indicated that from two to four 

 mixings are sufficient to enable operator to obtain constant 

 readings on the bridge. 



(d) Stock material is used throughout in the construction 

 and the cell is amply strong. 



In a modified form to be described at a later date, it is 

 proposed to describe a more compact type with spherical 

 bulbs of larger capacity for B and M, also a slightly modified 

 form for holder C. 



Department of Physics, 



Massachusetts Agricultural College, Amherst. 



