"Suitable organic solvents are, for example, aromatic hydrocarbons, such as xylene or mesitylene, and especially aliphatic or cycloaliphatic ketones, such as methyl isobutyl ketone, diisobutyl ketone, 2,4-dimethyl-6-heptanone, 2-heptanone, 3-heptanone, cyclopentanone, methylcyclopentanone, cyclohexanone and methylcyclohexanone." . . . . .