In such a mixed solvent containing at least a hydrocarbon, the ratio of alcohol (especially methanol) to other solvents (e.g., esters such as ethyl acetate, ethers such as tetrahydrofuran), the alcohol/other solvents ratio, by volume at 25??? C. is preferably of the order of 10/90 to 99/1, far preferably of the order of 30/70 to 98/2, further preferably of the order of 50/50 to 97/3.