As the water-soluble organic compound, for example, sugar alcohols such as glycerol and xylitol, amides such as dimethyl formamide, and dimethyl acetamide; ketones such as acetone; ethers such as tetrahydrofuran and dioxane; polyalkylene glycols such as polyethylene glycol and polypropylene glycol; alkylene glycols having an alkylene group of 2 to 6 carbon atoms such as ethylene glycol, propylene