SOME CHEMICAL REACTIONS IN SILICA GELS I. FORMATION OF MERCURIC IODIDE CRYSTALS1

This investigation was concerned with reactions which form Hgl2 in acidic gels pre-pared with acetic acid and sodium silicate. The results of this work support the postulation that the yellow crystal frontal zone which advances through the gel as reaction progresses is probably the yellow polymorph of Hgl2 and not a complex alkali metal mercuri-iodide. In addition, the results show that mercuric chloride reacts with iodine in acidic gels to form Hgl2. A plausible reaction scheme involving enhancement of I2 hydrolysis and enhancement of the disproportionation of HOI by the presence of Hg++ appears to explain this unanticipated behavior. The suitability of silica gels as a largely aqueous yet nonliquid diffusion-controlling medium for studying chemical reactions and for growing sizable crys-tals of difficultly soluble materials has been known for at least 50 years. A number of reactions in silica gels including the formation of mercuric iodide crystals (Holmes, 1917, 1934) have been studied in some detail. A classic experiment for growing mercuric iodide in an acidic silica gel con