The method of claim 9 wherein the nonionic surfactant is represented by the following formula: R--(OC2 H4)m --(OC3 H6)n --(OC4 H8)p --R1 ( 1) wherein R is an aliphatic hydrocarbon group containing from 8 to 15 carbon atoms; R1 is hydroxyl, chloride, C1 -C3 alkyl, C1 -C5 alkoxy or phenoxy; and m, n and p are numbers of from 0 to 30, the sum of m, n and p being from