organometallic compound that is the chief antiknock agent for automotive fuels. Manufactured by the action of ethyl chloride on a powdered alloy of lead and sodium, the compound is a dense, colourless liquid that is quite volatile, boiling at about 200° C (400° F). As an antidetonant (i.e., antiknock agent), tetraethyl lead is added to gasoline in quantities not exceeding 3 cubic cm (0.2 cubic inch) per gallon; a small quantity of ethylene dibromide and sometimes ethylene dichloride is added to prevent accumulation of lead deposits in the engine. Tetraethyl lead can cause acute or chronic lead poisoning if inhaled or absorbed through the skin. Its use declined markedly during the 1970s because the products of its combustion are toxic and detrimental to catalytic devices that were introduced to nullify other objectionable components of the exhaust gases of engines.