Fat and oil

   Fats and oils are esters of organic acids with glycerin. A very simple oil that is present in butter is glyceryl tributyrate:


   This is just a combination of butyric acid and glycerin:

                            O            HO-CH2
                            | |                    |
   CH2-CH2- CH2-C-OH      HO-CH

    butyric acid                      glycerin

   Most fats and oils are made from larger organic acid molecules; the oils are liquid at room temperature, and the fats are solid. Do not confuse oil, as used here, with petroleum oils.
Pure fats have no color, odor, or taste; these properties in natural fats arise from impurities. Common animal fats include lard from hogs and butterfat from cow's milk. Olive, peanut, corn, soybean, and palm oil are common vegetable oils. Many of these fats and oils are used in cooking, as is oleomargarine, which is a mixture of chiefly vegetable fats and oils.
   Fats and oils, particularly fish oils, are used as medicines and in the manufacture of animal feed. Oils are obtained from the herring, salmon, sardine, and sprat by boiling the fish and skimming the oil from the surface. An oil famous for its medicinal value is produced in the liver of the cod. Oil from the whale was a common fuel for lamps in the 19th century. Certain oils, called drying oils, harden after long exposure to air and are therefore used extensively in the paint industry. Linseed and cottonseed are the most common of these oils. These and other fats and oils are important raw materials in the manufacture of soap, lubricants, and candles.