Examples of particularly preferable organic solvents are polyhydric alcohols, e.g. glycerol, polyethylene glycol, propylene glycol; mixtures of one of these polyhydric alcohols and water, preferably 5-30% aqueous solutions of polyhydric alcohol; aqueous solutions of anionic, nonionic, or amphoteric surface active agents; alcohols, e.g. methanol, ethanol, butanol; mixtures of one of these alcohol a