Circa 500 . Cast iron was produced for the first time by the Chinese during the Zhou dynasty (1046-256 .). Prior to that, it had not been possible to raise the temperature of the ore sufficiently to melt the iron and the only available iron was wrought iron created by heating iron ore in a furnace with carbon as the reducing agent and hammering the resulting spongy iron output. Furnaces of the day could reach temperatures of about 1300°C which was enough to melt copper whose melting point is 1083°C but not enough to melt iron whose melting point is 1528°C. By a combination of the addition of phosphorus to the ore which reduced its melting point, the use of a bellows to pump air through the ore to aid the exothermic reduction process and the use of improved high temperature refractory bricks forming the walls of the furnace to withstand the heat, the Chinese were able to melt the iron and cast it into functional shapes ranging from tools and pots and pans to heavy load bearing constructional members as well as fine ornamental pieces.
Working memory is generally considered to have limited capacity. The earliest quantification of the capacity limit associated with short-term memory was the magical number seven introduced by Miller (1956). He noticed that the memory span of young adults was around seven elements, called chunks, regardless whether the elements were digits, letters, words, or other units. Later research revealed that span does depend on the category of chunks used (., span is around seven for digits, around six for letters, and around five for words), and even on features of the chunks within a category….Several other factors also affect a person’s measured span, and therefore it is difficult to pin down the capacity of short-term or working memory to a number of chunks. Nonetheless, Cowan (2001) has proposed that working memory has a capacity of about four chunks in young adults (and fewer in children and old adults).