Soap comprises the sodium or potassium salts of various fatty acids, but chiefly of oleic, stearic, palmitic, lauric, and myristic acids. For generations its use has increased until its manufacture has become an industry essential to the comfort and health of civilized human beings. The relative an industry essential of soap and detergents is shown increased.
Tallow is the principal fatty material in soap making, the qualities used represent about three-fourths of the total oils and fats consumed by the soap industry. It contains the mixed glycerides obtained from the solid fat of cattle by steam rendering. This solid fat is digested with steam; the tallow forms a layer above the water, so that it can be easily be removed. Tallow is usually mixed with coconut oil in the soap kettle or hydrolyzer in order to increase the solubility of the soap. Grease (about 20% percent) are the second most important raw material in soap making. They are obtained from hogs and smaller domestic animals and are an important source of glycerides of fatty acids. They are refined by steam rendering or by solvent extraction and are seldom used without being blended with other fats. In some cases, they are treated so as to free their fatty acids, with are used in soap instead of the grease itself. Coconut oil has long been important. The soap from coconut oil is firm and lather well. It contains large proportions of the very desirable glycerides of lauric and many other industries. The acidification of “foots,” or stock resulting from alkaline refining of oils, also produces fatty acids. The important general methods of splitting are outlined in the Twitcell process. Continuous cuntercurrent process are now most commonly used.
The soap maker is also a large consumer of chemicals, especially caustic soda, salt, soda ash, and caustic potash, as well as sodium silicate, sodium bicarbonate, and trisodium phosphate. Inorganic chemicals added to the soap are the so-called builders. Important work by Harris of Monsanto and his coworkers demonstrated conclusively that, in particular, trisodium pyrophosphate and sodium tripolyphosphate were unusually effective synergistic soap builders. Of considerable economic importance was the demonstration that combinations of pyrophosphate or sodium tripolyphosphate, were sometimes superior to the phosphate used alone. It was further shown that less soap could be used in these mixtures to attain the same or more effective soil removal.