Examples of the solvents are aliphatic hydrocarbons such as hexane, heptane, octane and decane, aromatic hydrocarbons such as toluene and xylene, alicyclic hydrocarbons such as cyclohexane, methylcyclohexane and decalin, and ether compounds such as diethyl ether, dibutyl ether, di-i-amyl ether and tetrahydrofuran.