A variable-volume cell was designed, built and validated to measure the solubility of salts in liquid ammonia, using a polythermal method at high pressure. The apparatus is based on a cell made of stainless steel and fitted with a sapphire window to allow the solubility process to be visually controlled. The solubility of three systems was measured: lithium nitrate in water at atmospheric pressure, lithium nitrate in ammonia at 20 bar and sodium thiocyanate in ammonia, also at 20 bar. An image processing treatment was also tested as a new procedure for detecting the solubility temperature. (C) 2013 Elsevier B.V. All rights reserved.