Automobiles dramatically changed life in the United States with their invention in the late nineteenth century. One of the negatives of automobiles, however, was a persistent and loud knocking sound in automobile engines. In 1916 Charles F. Kettering, founder of Delco, hired Thomas Midgley, Jr. to eradicate the persistent knocking sound. Midgley quickly discovered that the knocking sound resulted from the gasoline currently being produced in the United States. Several more years of research led Midgley to discover that placing tetraethyl lead additives in the gasoline would eliminate the knocking sound. Midgley patented this new version of gasoline, ethyl gasoline, on December 9, 1921. Unfortunately, the lead caused deposits to form on engine valves, causing engines to cease operating. Midgley then added ethylene dibromide to ethyl gasoline, which prevented the lead deposits. This new version of ethyl gasoline was sold for the first time on February 2, 1923 in Dayton, Ohio. Unfortunately, leaded gasoline proved harmful for the environment, and today leaded fuel is no longer used.