15th Century-- Leonardo DeVinci writes that air has several constituents, one of which supports combustion.
17th Century-- Robert Boyle provides the first operational definition of an element. Also, Boyle observes that for a given number of moles of gas molecules, the pressure is inversely proportional to the volume if the temperature is held constant.
1775-1776-- Antoine-Laurent Lavoisier first recognizes oxygen as an element.
1800-- Jacques Charles observes that, for a given number of moles of gas, the volume is directly proportional to the absolute temperature if the pressure is held constant.
1811-- Amedeo Avagadro proposed that equal volumes of a gas at constant pressure and temperature have an equal number of molecules.
Spring 1851-- Dr. John Gorrie invents the first working refrigerator.
1871-- Mendeleev's periodic table is published in English. Many empty spaces appear where soon-to-be discovered elements will be placed.
June, 1918--General Motors begins manufacturing refrigerators for purchase by the general public.
December 31, 1928-- The first patent is given for the formula for chlorofluorocarbons (CFC).
April 1930-- Midgley makes a presentation demonstrating the safety of CFCs.
August 27, 1930-- General Motors and DuPont enter into a joint venture to produce and market CFCs.
1932-- The Carrier Corporation markets the first self-contained household air-conditioning unit, "The Atmospheric Cabinet."
September 8, 1941--Thomas Midgley Jr. receives the American Chemical Society's Priestly award for outstanding creativity in the field of chemistry.
1956-- America's first air-conditioned mall opens in Edina, Minnesota.
December 1973-- Rowland and Molina theorize that CFCs can destroy the ozone in the stratosphere.
December l974--The first government hearings are held on the CFC-ozone theory in the United States.
August 1981--NASA scientist Donald Heath announces that satellite records show global ozone levels have declined 1 percent.
September 1987--The Montreal Protocol is signed, calling for eventual worldwide CFC reductions of 50 percent.
1990-1993-- DuPont's research and development arm produces substitutes for CFCs. These include partially hydrogenated chlorofluorocarbons(HCFC) and totally hydrogenated chlorofluorocarbons (HFC).
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