In Chinese mythology, Qi Yu is the god of rain, being a descendant of Shen Nong, the inventor of agriculture. His appearance is half giant, half bull, with the front of his head covered with (or made of) iron. Chinese mythology is the mythology of Chinese civilization. ... The term God is used to designate a Supreme Being; however, there are countless definitions of God. ... Rain is a form of precipitation, other forms of which include snow, sleet, hail, and dew. ... Shennong (Traditional: 神農; Simplified: 神农; Pinyin: Shen2 nong2) is a legendary emperor and culture hero of Chinese mythology who is believed to have lived some 5,000 years ago and who taught the ancient peoples of the practices of agriculture. ... General Name, Symbol, Number iron, Fe, 26 Chemical series transition metal Group, Period, Block 8 (VIIIB), 4, d Density, Hardness 7874 kg/m3, 4. ...
Though Yu Yan (zi Yuwu; hao Quanyang zi, Linwu shanren, and Shijian daoren; 1258-1314), a native of modern Suzhou, is sometimes indicated to have developed his interest in alchemy late in life, he wrote his Zhouyi cantong qi fahui (Clarification of the Zhouyi cantong qi; CT 1005) when he was in his middle twenties.
Yu Yan's references to them as "old text" is a further proof of their early date.
The Zhouyi cantong qi fahui is firmly rooted in the textual legacy of the Southern and Northern lineages of Song Taoism.