Abstract Irradiation of rubber sols with ultraviolet light in the absence of oxygen results in gelation under certain conditions. From a study of the reaction curves the mechanism of this reaction was shown by the authors in a previous paper to consist mainly of a three-dimensional polymerization. The curves were derived by following the reaction by means of viscosity measurements, in the presence of an accelerator, benzophenone, with carbon tetrachloride as solvent. It was deemed of interest to compare these curves with those obtained without the use of benzophenone, and the experimental work described in the following deals with the study of the reaction in the absence of accelerators. The products obtained on removing the solvent from photogels differ markedly for various solvents, but are in all cases insoluble and show elastic properties similar to those of lightly vulcanized rubber. The solvents used are of two types, active and inactive. In the case of the active ones, such as carbon tetrachloride, the solvent molecules condense with the rubber, and on removal of the solvent from the resulting photogels, the products are often considerably heavier than the original rubber samples. When carbon tetrachloride is used, the reaction product has been shown to contain appreciable amounts of combined chlorine. With inactive solvents like benzene, ligroin, etc., no increases in weight are observed and gels are generally formed less readily.