P 2388 (OTTO) Potassium nitrate, 99.999% Cas 7757-79-1 - used for niter bluing, which is less durable than other forms of protective oxidation, but allows for specific and often beautiful coloration of steel parts, such as screws, pins, and other small parts of firearms. P 2388 (OTTO) Potassium nitrate, 99.999% Cas 7757-79-1 - used as an electrolyte in a salt bridge, and as thermal storage medium in power generation systems. It forms phase change material with silica and alumina nanoparticles.