||ULTRAVIOLET ABSORBANCE - measurement of the ultraviolet absorption of petroleum products, determined by standardized tests, such as ASTM D 2008. Aromatics absorb more ultraviolet light than do naphthenes and paraffins, and the amount of absorbance can be used as an indication of the amount of aromatics in a product. Certain polynuclear aromatics (PNA’s) are known carcinogens (cancer-causing substances), with peaks of absorbance generally between 280 and 400 millimicrons. The Food and Drug Administration (FDA) has therefore imposed limits on the amount of ultraviolet absorbance at these wavelengths for materials classified as food additives. However, not all materials with ultraviolet absorbance at these wavelengths are carcinogenic.
UNLEADED GASOLINE - gasoline that derives its anti-knock properties from high-octane hydrocarbons or from non-lead anti-knock compounds, rather than from a lead additive. See lead alkyl.
UNSATURATED HYDROCARBON - hydrocarbon lacking a full complement of hydrogen atoms, and thus characterized by one or more double or triple bonds between carbon atoms. Hydrocarbons having only one double bond between adjacent carbon atoms in the molecule are called olefins; those having two double bonds in the molecule are diolefins. Hydrocarbons having alternating single and double bonds between adjacent carbon atoms in a benzene-ring configuration are called aromatics. Hydrocarbons with a triple bond between carbon atoms are called acetylenes. Unsaturated hydrocarbons readily attract additional hydrogen, oxygen, or other atoms, and are therefore highly reactive. See hydrocarbon, saturated hydrocarbon, hydrogenation.
USP (UNITED STATES PHARMACOPOEIA) - compendium of drugs, drug formulas, quality standards and tests published by the United States Pharmacopoeia Convention, Inc., which also publishes the NF (National Formulary). The purpose of the USP is to ensure drug uniformity and to maintain and upgrade standards of drug quality and purity, as well as establish packaging, labeling, and storage requirements. The USP includes standards for white oils under two classifications: “Mineral Oil” for heavy grades, and “Mineral Oil Light” for lighter grades.