carbon atoms; (b) the salt of (1) an interpolymer having the structure ##STR7## wherein R and R1 are members of the group consisting of hydrogen and methyl, R2 is a member of the group consisting of methyl and ethyl; n represents from 3 to 12 weight percent based on the combined weight of n, x, y and z, x represents from 8 to 25 percent based on the combined weight of n, x, y and z; y represents f