Chlorofluorocarbon: Chlorofluorocarbon (CFC), any of several organic compounds composed of carbon, fluorine, and chlorine. When CFCs also contain hydrogen in place of one or more chlorines, they are called hydrochlorofluorocarbons, or HCFCs. CFCs are also called Freons, a trademark of the E.I. du Pont de Nemours & Company in Wilmington, Del. CFCs were originally developed as refrigerants during the 1930s. Some of these compounds, especially trichlorofluoromethane (CFC-11) and dichlorodifluoromethane (CFC-12), found use as aerosol-spray propellants, solvents, and foam-blowing agents.
The Egyptians started building the Great Pyramid of Giza on August 23, 2470 B.C., according to controversial new research that attempts to place an exact date on the start of the ancient construction project. Enlarge Photo. Printer Friendly. Email to a Friend.
The ancient Egyptians built large and elaborate pyramids as tombs for their kings, the pharaohs. They were built of huge stone blocks and took a couple of decades to build. The three pyramids of Giza are the most famous. They were built in the 26th century B.C. The largest pyramid of Giza is called the Great Pyramid of Khufu. It is also the largest and grandest pyramid ever built. It is 479 feet tall (146 meters). The pharaoh Sneferu built this pyramid for his son, Khufu, in 2540 B.C. It was built from millions of blocks of limestone and granite.