Competitive binding of calcium ions by combinations of soap and deterg
ent builders viz., sodium tripolyphosphate (STPP), tetrasodium pyropho
sphate (TSPP) and ethylene diamine tetraacetic acid (EDTA) was studied
in model systems as well in formulated toilet soaps. Studies on model
systems indicated that the distribution of calcium ions between the s
oap and builder is a function of the ratio of the concentration of the
soap and builder. During the initial stages of the interaction of cal
cium ions with the combinations of soap and builder, formation of Ca-b
uilder complex predominates while over longer intervals of time (under
''equilibrium conditions'') calcium soap formation takes over.