A handy method for measuring the concentrations of acid and metallic ion in pickling solution has been developped by using the conductivity-specific gravity diagram (c-d diagram). The standard c-d diagrams were made in advance by measuring the conductivity and specific gravity of a standard solution in the presence of ferrous ion and zinc ion at various temperatures. Utilizing the c-d diagrams together with the temperature correction graph, the errors of measurement were reduced to 5.9% for acid concentrative and 18.9% for metallic ion concentration.

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