Red to dark red powder. Copper and iron dull color; iron to a greater extent. Azo dyes in powder form can be explosive when suspended in air at specific concentrations. Moderately soluble in water to give acidic solution. Aqueous solutions react as acids to neutralize bases in weakly exothermic reactions. Toxic gases are formed by mixing with acids, aldehydes, amides, carbamates, cyanides, inorganic fluorides, halogenated organics, isocyanates, ketones, metals, nitrides, peroxides, phenols, epoxides, acyl halides, and strong oxidizing or reducing agents. Flammable gases are formed by mixing materials in this group with alkali metals. Explosive combination can occur with strong oxidizing agents, metal salts, peroxides, and sulfides.