Abstract: We synthesized 1,8-dihydroxy-3,6-dithiaoctane (DTO) and studied its accelerating effect towards the crystal growth during emulsification and physical ripening and its effect on sensitometric properties of silver halide emulsions.1. Prom UV and NMR spectra it can be seen that the valence bridge -S-CH₂-was formed and the synthesized compound has the following structure: HO-CH₂-CH₂ -S-CH₂-CH₂-S-CH₂-CH₂-OH.2. The electron micrographs demonstrate that in absence of DTO the silver halide grains consist of two different parts: one is fairly large, the other ia quite small. When 0.18-0.35 g/molAgBr of DTO is added, a great change in grain size distribution is taken place. When the amount of DTO is increased to 0.5 g/molAgBr, the small grains disappeared practically, all grains became more homogeneous and the average grain size in Fig. 3(B) is shown to be much larger than that in Pig. 3(A), though the biggest grain in Pig. 3(B) seems smaller than that in Pig. 3(A).3. Sensitometric properties can be seen from table 1. With the increase of the amount of DTO the fog increased step by step, sensitivity increased first, through a plateau, later droped to the original value again. The same case was with the contrast.4. Ionic conductivity can be seen from table 2. The addition of DTO ia characterized by the phenomena and its addition has no effect practially on pBr and pH of the emulsion, which is different from other solvent, such as Br^-, ONS^-, and ammonia. With the increase of the amount of DTO log f_max shifts to the range of lower frequency. The log f_max drops from 5.5 to 4.7. This difference in ionic conductivity may be used partly to account for the sensitometric property change of emulsion with the solubiliz-ing effect of DTO.