Gelatin forms a viscous solution when dissolved in hot water, which sets to a gel on cooling. Gelatin added directly to cold water does not dissolve well. Gelatin is also soluble in most polar solvents. Gelatin solutions show viscoelastic flow and streaming birefringence. The solubility of the gelatin is determined by the method of manufacture. Typically, gelatin can be dispersed in a relatively concentrated acid. Such dispersions are stable for 10–15 days with little or no chemical changes and are suitable for coating purposes or for extrusion into a precipitating bath.