Thermoanalytical and other evidence shows that methanol, acetone and some other organic liquids are strongly sorbed by tricalcium silicate pastes, and cannot be completely removed by vacuum drying or heating at temperatures that do not profoundly alter the material. This confirms an observation by Day (1981). When pastes that have been treated with these liquids are heated in nitrogen to 200° to 600°C, carbonate ion is formed; this seriously alters the thermogravimetric curve. Acetone, when sorbed in tricalcium silicate pastes, undergoes condensation reactions at room temperature. These conclusions have implications for the use of organic liquids to stop hydration or in the preparation of polished sections for X-ray microanalysis.