Coins of the pound sterling also became known as a "pound". (240 actual pennies, however, weighed only 5400 troy grains, known as tower pound, a unit used only by mints. The tower pound was abolished in the 16th century.) The silver penny remained the primary unit of coinage for about 500 years. The purity of 92.5% silver (i.e., sterling silver) was instituted by Henry II in 1158 with the "Tealby Penny" — a hammered coin. Over the years, the penny was gradually debased until by the 16th century it contained about a third the silver content of a proper troy 24 grain pennyweight. By 1915,
Five Grains behavior towards the Five Grains could take on political meaning: as a protest against the overthrow of the Shang Dynasty by the Zhou, Boyi and Shuqi ostentatiously refused to eat the Five Grains. Such rejections of the grains for political reasons underwent a complex development into the concept of "bigu", the esoteric Taoist practice of achieving immortality by avoiding certain foods. By the time of written records, the development of agriculture in China had become greatly mythologized. There were various traditions regarding which of the early Chinese leaders introduced the Five Grains: Shennong (神农) ( "Divine Farmer") was a Chinese