THE SUSPENDING POWER OF DETERGENT SOLUTIONS: II. SOAP-BUILDER SOLUTIONS

Abstract

Laboratory scale measurements have been made of the ability of certain alkaline salts, commonly used as laundry soap builders, to hold carbon particles in suspension, and thus prevent their deposition on fabric during the washing process. In the absence of soap little difference was noted between any of the builders studied, the suspending power being, on the whole, poorer than that of distilled water. In general, the addition of builders to soap solutions resulted in a decrease in the suspending power of the soap, this effect increasing with increasing builder concentration. The builders fall into three general classifications, viz.: simple electrolytes, silicates, and phosphates. Within each of these groups of builders the suspending power of a built soap solution increases with decreasing pH of the solution. A tentative explanation of the influence of added builders on the suspending power of soap solutions is offered, on the basis of interference with the normal adsorption of soap by the carbon particles, and, in some cases, the superimposed adsorption of the anion of the builder. Classification of the builders with respect to their effect on the suspending power of various pure soaps indicated that sodium hexametaphosphate is superior to all others, while sodium hydroxide and sodium orthosilicate are the poorest. There are only minor differences between the remaining builders, tetrasodium pyrophosphate and trisodium phosphate being the best in this group. This classification, which is based solely on suspending power, is not necessarily indicative of the over-all efficiency of builders in the detergent process as a whole.