42 INSTRUMENTATION IN SCIENTIFIC RESEARCH [Chap. 1 



real improvement of the transducer can be expected from variations 

 of the construction or of the carbon composition unless more is 

 known about the physical mechanism causing the resistance-varia- 

 tion effect. 



e. Electrolytic Displacement Transducers. The resistance between 

 two electrodes in contact with an electrolyte depends upon the 



Moving electrode 



Paraffin oil 

 -Electrolyte 



- Mercury 



Fig. (1-2)23. Electrolytic dis- 

 placement transducer [M. 

 Manzotti, J. Set. Instr., 33, 314 

 (1956); by permission]. 



Rubber hose 



L 



Electrolyte 



Electrode ' 



Fig. (1-2)25. Simple electrolytic dis- 

 placement transducer. 



Eixed electrode 



Electrolyte (alcohol -glycerine) 

 held in glass by capillary forces 



Moving electrode 

 =o 



Fig. (1-2)24. Electrolytic displacement 

 transducer [B. S. Gunther and J. B. 

 Concha, Proc. Soc.Exptl. Biol. Med., 69, 

 302(1948); by permission]. 

 B, B 2 



x L 



Fig. (1-2)26. Electrolytic displace- 

 ment transducer used for pressure 

 measurements. B x , B 2 , insulating 

 bodj-; A, annular chambers; J5 1 , E{ , 

 E 2 , E' 2 , electrodes and pressure ducts; 

 M, membrane; G, resistance gap 

 [from J. R. Pappenheimer, Rev. Sci. 

 Instr., 25, 912 (1954); by jwrmission]. 



geometry of the conducting path; any change of the length or the 

 cross-sectional area of the conductive path causes a variation of the 

 resistance. 



A great number of electrolytic displacement transducers have been 

 described in the literature, particularly in the field of physiology. 

 Figures (1-2)23 to (1-2)26 show different constructions of such trans- 

 ducers. 



