structural:scholar_edition, structural:reformatting
Metallurgy and Engineering

The Iron Pillar of Delhi high resistance to corrosion. The corrosion resistance results from an even layer of crystalline iron(III) hydrogen phosphate hydrate forming on the high- phosphorus -content iron, which serves to protect it from the effects of the corrosion The earliest evidence of the cotton gin was found in the fifth century, in the form of Buddhist paintings depicting a single-roller gin in the Ajanta Caves. The gins consisted of a single roller made of iron or wood and a flat piece of stone or wood.