The solubility of sodium azide was determined in water and in 40, 60, 80, and 95.5% ethanol-water mixtures, respectively. The solubilities were first determined by a synthetic method (9) which involved the preparation of a solution of known composition, the saturation point of which was determined by varying the temperature. The colorimetric method employing the 462-mp band of the ferric azide complex ( 1 ) was not useful in this case because of the dependence of the absorbance values on pH. A precise control of the p H was necessary, and the method was applicable only in aqueous media. A gravimetric procedure involving the evaporation of the solvent and baking of the residue was the most reliable and accurate method for the determination of the solubility of sodium azide in the solvents used. The flame photometric method gave results in agreement with the gravimetric procedure. The solubility of alpha-lead azide was determined in water and in 5,10, and 15% sodium and ammonium acetate solutions, respectively. The spectrophotometric procedure (1) was employed in view of the extreme thermal sensitivity of lead azide. Care w&s taken to keep the p H constant at 2.2.