在《国语·齐语》中，记载着管仲对齐桓公说的一句话：“美金以铸剑戟，试诸狗马；恶金以铸钼、夷、斤，试诸壤土。”这里美金指的就是青铜，恶金指的则是铁。
春秋战国以后随着铁制农具的出现，农业生产对季节性的要求更高了，就逐渐形成了节气的概念。
During the Spring and Autumn Period, the agricultural production was highly subject to the seasonal changes with the invention of iron tools, thus forming the concept of Solar Term.
农民用买来的工具生产出的等价商品交换铁制的和木制的农具。
Metal and wooden tools are purchased with a commodity of equal value, produced using the tools acquired by the trade.
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