ASPECTS OF CHEI,ATION IN COSMETIC PRODUCTS 100 200 7_00 -- •50-- 100- 50-- Mo/e Na•oeDTA O. ! • $od/•,m stearate o I I 20 60 100 140 180 220 260 Go. CO 3 HARDNESS, PPM Figure 3.--CaCOa vs. foam height. 267 Foaming of stearate or any soap solutions is pH dependent and a very sharp break in the standard foam curve occurs between 100 and 200 p.p.m. CaCOa when a 0.1 per cent solution of sodium stearate with the pH adjusted to 10.0 is investigated. Figure 3 shows the protective action of EDTA for such a dilute soap solution. At 0.5 mole EDTA to a mole of hardness, EDTA effected 84 per cent regeneration of the predicted foam height. At a mole to mole ratio 100 per cent regeneration was obtained. None of the dehydrated phosphates generated any foam at all even at mole ratios to hardness of 10 to 1. Since chelating agents are sold on a chelation performance toward CaCOa, one can easily calculate the required amount to add to any soap or

268 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS • /go • loo 6o 4o oeo o Figure 3a. syndet-based shampoo for any desired softening action. Taking the average shampoo application as one fluid ounce we have 35.4 gm. of solu- tion, and 1 per cent of this solution is Versene acid (EDTAA) solubilized with a suitable base and buffered to the pH of the shampoo, then 0.354 gm. of Versene acid is present in the applied solution. Since 1 gm. of Versene acid chelates 339 mg. CaCOa, the 0.354 gm. will chelate 120 mg. CaCO•. This amount in the applied shampoo would have the capacity to soften one liter of water having a hardness of 120 p.p.m. CaCOa or the equivalent of 7 gin. per gallon hardness A standard EDTA-CaC12 titration for water softening capacity could be employed for quality control of either soap of syndet shampoo. In the case of TEA soaps the tetrasodium derivative of EDTA can be added during the saponification or neutralization without much change in the pH of the preparation. With syndets, either the potassium or triethanolamine derivative of EDTA can be used to affect compatibility and close control of pH. The use of EDTA alone or in combination with a lime soap dispersing agent may be the means of improving the performance of bar soap in hard water areas. Medicated deodorant and beauty bar soaps that demand a premium can justify higher percentages of EDTA for greater hardness