Coal the heat and pressure of deep burial causes the loss of water, methane and carbon dioxide and an increase in the proportion of carbon. Thus first lignite (also called "brown coal"), then sub-bituminous coal, bituminous coal, and lastly anthracite (also called "hard coal" or "black coal") may be formed. The wide, shallow seas of the Carboniferous Period provided ideal conditions for coal formation, although coal is known from most geological periods. The exception is the coal gap in the Permian–Triassic extinction event, where coal is rare. Coal is known from Precambrian strata, which predate land plants—this coal is presumed to
Central Scientific Company bombsights for airplanes and fuses for large bombs. After 1968, the company began having financial difficulties. In 1974, the assets were sold off to competitors. The educational business retained the name Central Scientific Company. In April 1979, Central Scientific's assets and activities were acquired by two businessmen from Buffalo, New York. They sold the business to Sargent-Welch (their main competitor) in 2000. Central Scientific Company Central Scientific Company was founded in 1900 in downtown Chicago. It was formed out of what was left of the Olmstad Scientific Company. Central Scientific manufactured and distributed science teaching equipment for schools, colleges, and