Kinetics of the formation of monodispersed sulfur sols from thiosulfate and acid

Abstract

1. 1. The optical absorption of 0.0015 M NaHSO 3, Na 2S 2O 3, and Na 2S 4O 6, in aqueous solution and of sulfur (0.001-0.003 M) in CHCl 3, CCl 4, CH 3COCH 3 and CS 2 have been measured with the Beckman quartz spectrophotometer, model DU, over the range λ = 390 to 270 mμ. The ions do not absorb above λ = 300 and sulfur does not absorb above 390 mμ. Hence the absorption at λ = 300 can be used to determine sulfur in the presence of these ions. 2. 2. The transmittance of mixtures of dilute thiosulfate and acid has been studied as a function of the time elapsing after mixing at wave lengths of 300, 435 and 560 mμ. 3. 3. The solutions remain crystal clear in the visible (λ = 435 and 560 mμ) for a period of time which depends upon the initial concentrations of acid and of thiosulfate. During this period, however, the transmittance at λ = 300 shows conclusively that sulfur is being continuously formed during the homogeneous period of this reaction. Coincident with the visual appearance of a Tyndall beam, the optical density curves ( log I 0 I ) at all wave lengths exhibit a discontinuity, which is interpreted as corresponding to the formation of discrete sulfur particles from the supersaturated homogeneous solution of sulfur in water. 4. 4. Although the time of appearance of the Tyndall beam depends upon the initial concentrations of thiosulfate and acid, the optical density at that time remains constant, indicating that the transition from true solution to colloidal dispersion of sulfur occurs at a fixed value of supersaturation of sulfur in water, which corresponds approximately to 5 × 10 −6 g.-atoms of sulfur/1, of water. 5. 5. Insofar as this method of preparing monodisperse colloids has been investigated, the results are in harmony with von Weimarn's conclusions on “corresponding crystallization conditions.” We intend shortly to discuss the results in terms of the more elaborate theory of Becker and Doering ( Ann. Physik 24, 719 (1935)).