Heavy metals are here treated as light metals and, in general, are not further considered. The heaviness of naturally occurring metals such as gold, copper, and iron may have been noticed in prehistory and, in light of their malleability, led to the first attempts to craft metal ornaments, tools, and weapons. All metals discovered from then until 1809 had relatively high densities; their heaviness was regarded as a singularly distinguishing criterion. From 1809 onwards, light metals such as sodium, potassium, and strontium were isolated. Their low densities challenged conventional wisdom and it was proposed to refer to them as "metalloids" (meaning "resembling
Permanente Metals short tons of goop-filled bombs were used in World War II (approximately eight percent of the total tonnage of incendiaries that were dropped during that conflict). Permanente ranked 42nd among United States corporations in the value of World War II military production contracts. Permanente Metals Permanente Metals Corporation (PMC) is best known for having managed the Richmond Shipyards in Richmond, California, owned by one of industrialist Henry J. Kaiser's many corporations, and also engaged in related corporate activities. These four of the seven west coast Kaiser Shipyards were known for their construction of Liberty ships. The company was also a