GLYCEROL , propane-1,2,3,-triol, glycerin (USP), a trihydric alcohol, is a clear, water-white, viscous, sweet-tasting hygroscopic liquid at ordinary room temperatures above its melting point. Glycerol was first discovered in 1779 by Scheele, who heated a mixture of litharge and olive oil and extracted it with water. Glycerol occurs naturally in combined form as glycerides in all animal and vegetable fats and oils, and is recovered, as a by-product when these oils are saponified in the process of manufacturing soap, when the fats are split in the production of fatty acids, or when fats are esterified with methanol in the production of methyl esters. Since 1949 it has also been produced commercially by synthesis from propylene [115-07-1]. The latter currently accounts for ca 30% of United States production.The uses of glycerol number in the thousands, with large amounts going into the manufacture of drugs, cosmetics, toothpastes, urethane foam, synthetic resins, and ester gums. Tobacco processing and foods also consume large amounts either as glycerol or glycerides. 1 2 GL YCEROLby the names 2-aceto-3-palmito-1-stearin,-2-aceto-3-stearo-1-palmitin, and 3-palmito-1-stearo-2-acetin. Any one of the three acids can be given the -in termination; if possible, this acid receives the locant 1. The other acids are cited in alphabetical order (regardless of carbon content) and numbered, if there is a choice, to give the lowest possible numbering (see also Carboxylic acids; Esters, organic). PropertiesPhysical properties of glycerol are shown in Table 1. Glycerol is completely soluble in water and alcohol, slightly soluble in diethyl ether, ethyl acetate, and dioxane, and insoluble in hydrocarbons (1). Glycerol is seldom seen in the crystallized state because of its tendency to supercool and its pronounced freezing point depression when mixed with water. A mixture of 66.7% glycerol, 33.3% water forms a eutectic mixture with a freezing point of −46.5 • C .Glycerol, the simplest trihydric alcohol, forms esters, ethers, halides, amines, aldehydes, and such unsaturated compounds as acrolein (qv). As an alcohol, glycerol also has the ability to form salts such as sodium glyceroxide (see also Alcohols, polyhydric).