Water-soluble organic solvents that can be used for the purpose of the invention include alkyl alcohols having 1 to 4 carbon atoms such as methyl alcohol, amides such as dimethylformamide, ketones and ketone alcohols such as acetone, ethers such as tetrahydrofuran, polyaklylene glycols such as polyethylene glycol, alkylene glycols whose alkylene group has 2 to 6 carbon atoms such as ethylene glyco