A solvent used in the operation of the reprecipitation described above includes, for example, aliphatic hydrocarbons such as pentane, hexane and the like; cyclic hydrocarbons such as cyclohexane and the like; aromatic hydrocarbons such as benzene, xylene and the like; halogenated hydrocarbons such as methylene chloride, chloroform, chlorobenzene, dichlorobenzene and the like; nitrated hydrocarbons