from 0.1 to 10% by weight of {HEAD ~ a compound} of {TAIL ~ formula} : ##STR3## wherein the individual radicals R are identical are each a C1 C12 alkyl group or a polyoxyethylene radical which contains 1 to 6 ethylene units and whose terminal OH group is methylated; and 
of
from 0.1 to 10 % by weight of { HEAD ~ a compound } of { TAIL ~ formula } : # # STR3 # # wherein the individual radicals R are identical are each a C1 C12 alkyl group or a polyoxyethylene radical which contains 1 to 6 ethylene units and whose terminal OH group is methylated ; and
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH