A general discussion about the method of colloid titrations is given in this report. A new titration method is based on the stoichiometric combination of positive and negative colloid ions. The end point is decided by indicators (known as metachromatic coloring matters) like toluidine blue. The standard colloid reagents are P.V.S.‐K (potassium salt of polyvinyl alcohol sulfate) and Macramin (N‐polymethylated chitosan derivatives). The typical operations of this method are described briefly: the direct, indirect, and differential titration methods. The colloid titration curve is somewhat different from the acid‐base titration curve obtained potentiometrically, but it is characteristic and reproducible under definite conditions and so it is useful in quantitative and qualitative analysis. This titration may be carried out even under extraordinary dilute conditions (5 × 10−4 N) and the entire process is quite similar to the usual acid‐alkali titration. The precision is below ±ca. 5% if the method is carefully followed.

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Therapeutic Level IV.

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