Abstract The solvent used in the recrystallization of a solid may be determined by use of the IR spectrum and gas cell. Recrystallized powders retain a minute amount of solvent which is not detectable in a KBr disk of the powder, but is detectable when a gas cell is vised. The following solvents were examined by this method: acetone, benzene, n-butanol, tert-butanol, carbon tetrachloride, chloroform, ethanol, ethyl acetate, ethyl ether, isopropyl alcohol, methanol, n-propanol, trichloroethylene, toluene.