Examples of water-soluble organic solvents that can be used for the purpose of the present invention include alkyl alcohols having 1 to 5 carbon atoms such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol, isobutyl alcohol and n-pentanol, amides such as dimethylformamide and dimethylacetoamide, ketones and keto-alcohols s