The fact that characteristic crystalline products result upon the diffusion of arsenate ions into silicic acid gel which has been impregnated with stannous ions has been known by the Pacific Chemistry Department for some time. The optimum conditions with regards to heat and hydrogen ion concentration have been determined. The purpose of this investigation was to study the products of the reaction. First to determine whether or not the silicic acid itself combined with the stannous and arsenate. ions in the formation of the crystalline product, and second to determine its chemical composition.