Electrical measurementsA laboratory manual . Fig. 48. These conductivities are relative compared with mer-cury at 0° C. But the specificconductivity of mercury is 1063X 10 ~^ units. Hence theconductivity of the above solu-tions in units may befound by multiplying the valueof k by 1063X10-\ To measure the conductivity ofany liquid one of the standardsolutions is iirst placed in theappropriate vessel (Fig. 48), de-signed by Kohlrausch. It is wellto be provided with several of these vessels, with connecting tubes of different cross-section, adapted toliquids of differentconductivity
Electrical measurementsA laboratory manual . Fig. 48. These conductivities are relative compared with mer-cury at 0° C. But the specificconductivity of mercury is 1063X 10 ~^ units. Hence theconductivity of the above solu-tions in units may befound by multiplying the valueof k by 1063X10-\ To measure the conductivity ofany liquid one of the standardsolutions is iirst placed in theappropriate vessel (Fig. 48), de-signed by Kohlrausch. It is wellto be provided with several of these vessels, with connecting tubes of different cross-section, adapted toliquids of differentconductivity. The electrodes areplatinized platinum,with their lower sur-faces convex. Letthis liquid resist-ance be connected inone of the arms ofthe bridge, as Mi(Fig. 49), and leti^2, Ms J and Mi benon-inductive resist-ances. The contin-uous lines indicatepermanent connec-tions inside the com-mutator box, the. Fig. 49. 112 ELECTEICAL MEASUREMENTS. dotted lines temporary connections outside. Then if thecommutator is rapidly rotated the circuit through thegalvanometer is reversed simultaneously with thatthrough the battery and resistances. Hence the cur-rents through the galvanometer are rendered uni-directional. The resistances are then adjusted to balance, and thesame relation subsists between them as in the case ofsteady currents. Next, fill the vessel with the electro-lyte to be measured and balance as before. The ratio ofthe two resistances will be the relative resistance of thetwo liquids, and their conductivities will be inversely asthese resistances. Example. Standcard solution: NaCl, spec. grav. at 18° C. Let kx equal the conductivity to be measured. The electrolytewas jjlaced in one arm of the bridge, and two incandescent lampsin another. Two resistance boxes, A and B, were in the otherarms. Call the resistance of the lamps R. Then if r and r arethe resistances of the two sol
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