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Electrical Conductivity

Solutions of electrolytes can conduct electric current due to the presence of electrolytes under the influence of an electric field.

Definition: Electrical conductivity may be defined as a measure of the ability of a solution to carry electric current. This conductance is obeyed by ohm’s law and is measured by specific resistance.

Theory: Specific resistance is defined as resistance in ohms of a column of solution 1 cm long and 1sq cm in cross-section. The conductivity or specific conductance is the reciprocal of specific resistance. It is expressed as reciprocal ohms (i.e., ohms _ 1 or mhos)

Measurement of Electrical Conductivity: The electrical conductivity is measured in terms of specific conductance which is reciprocal of specific resistance. The specific conductance is estimated from the resistance obtained from the filled solution in the cell. The electric resistance of milk is measured by placing milk in a cell, between two platinum electrodes fixed at a distance. The electrical resistance is measured with the help of Wheatstone bridge. The specific conductance is calculated from the measured resistance of the cell filled with solution e.g. milk.

Thus

Specific conductance =K/R

Where K= cell constant determined with cell of solutions of known conductance and R = measured resistance in ohms.

Specific Conductance of milk: The specific resistance of milk is low with an average value of 0.005 ohm -1 . During mastitis the value increases due to the presence of various ions of milk. The various ions responsible for the conductivity of milk are sodium, potassium and chloride ions. In mastitis and colostrum milk these ions are abnormally high. .

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