Relatively high concentrations of silica sometimes occur in hydrothermal waters with polymerization and precipitation upon cooling. In slightly basic solutions silicic acid ionizes to form monosilicates and sometimes polysilicates. The ionization behavior and polysilicate formation are best studied by precise potentiometry using cells such as were developed at ORNL in programs supported by the Division of Physical Research of ERDA. they have nearly completed the experimental part of a detailed study of some of these equilibria using titration techniques in a hydrogen-electrode concentration cell to examine polysilicate formation in 1 m NaCl solutions at temperatures from 60 to 290 C and at Si(IV) concentrations 0.005 m to 0.05 m. At the lowest concentration only mononuclear species occur over wide temperature and pH ranges. At hydroxyl numbers from about 0.6 to 1.0 (average charge-per-silicon) small polysilicates which equilibrate rapidly occur at higher Si(IV) concentrations. A re-examination of the early work of Ingri at 25 C is described as well as conclusions regarding the most probable formulas of the polysilicates in the basic solutions
