Measurement of Electric Conductivity

Principle of Salt Bridge:

In salt bridge 2 fixed the resistance R1 and R2 and variable resistance Rv are connected in a branched circuit with the conductance cell having resistance Rx. An AC potential is applied at C and D. An AC potential is employed to prevent electrolysis of the solutions and polarization of electrode in the conductance at Rx. Ordinarily 1000 cycle source. As the frequency arises, capacitance effects become important and are compared for which the variable condenser in paralledl wih R2. the variable resistance by Rv is adjusted until there is no current pain the phone circuit from A to B as indicated by a minimum shadow or shift in the electric eyes.

There A and B are at the same potential and the voltage drop. IRX between BD must b equal to I’R2 the voltage drop between Ad.

IRx = I’R2

Also, Irv= I/R

IRx/Irv= I’R2/ IR1,

Hence,

Rx= I’R2/I’R1 x Irv.

Since R1 and R2 are fixed, the dial on Rv can be calibrated to read Rx the resistance of the test sample or the dial on Rv can be calibrated to read I/Rx that is directly in conductance of the solution.

% salts in soil= EC (mmhos/cm) X 0.064