The CMC and the aggregation number of Triton X-100 in mixtures of ethylene glycol and water have been measured by surface tension and static flucorescence decay methods. The discontinuity of the surface tension curve indicates that Triton X-100 forms micelles in ethylene glycol, though its CMC (0.05mol·L-1, 20℃) is greater than that in water. From fluorescence decay the aggregation number of Trion X-100 in ethylene glycol is 25 (30℃) in comparison with 97 in water. The aggegation number is reduced by adding glycol into an aqueous solution of Trion X-100. These could be interpreted in terms of a more favourable interaction between molecules of glycol and Trion X-100 than between water and Trion X-100.
