The natural acids are rarely of a single type in any given fat or oil. In fact, a singletriglyceride molecule in a fat may contain three different acid residues (R1COOH, R2COOH,R3COOH), and not every triglyceride in the substance will be identical. Each fat or oil,however, has a characteristic statistical distribution of the various types of acids possible—Seechapter 26.3, pg 1121 of Bruice for some examples.The fats and oils that are most common in soap preparations are lard and tallow from animalsources, and coconut, palm, and olive oils from vegetable sources. The length of hydrocarbonchain and the number of double bonds in the carboxylic acid portion of the fat or oil determinethe properties of the resulting soap. For example, a salt of a saturated long-chain acid makes aharder, more insoluble soap. Chain length also affects solubility.Tallow is the principal fatty material used in making soap. The solid fats of cattle are meltedwith steam, and the tallow layer formed at the top is removed. Soapmakers usually blend tallowwith coconut oil and saponify this mixture. The resulting soap contains mainly the salts ofpalmitic, stearic, and oleic acids from the tallow, and the salts of lauric and myristic acids from the coconut oil. The coconut oil is added to produce a softer, more soluble soap. Lard (from hogs) differs from tallow (from cattle or sheep) in that lard contains more oleic acid.
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