Minerals and Metals in Ancient India v1.c27.s2.t2.34

v1.c27.s2.t2.34

According to Wranglén (1970), the deciding factor behind the rustlessness of the pillar is the dry and unpolluted climate of the Delhi area particularly during the 1500 years up to the beginning of this century. The atmosphere has low relative humidity which rarely exceeds the critical 70 per cent (the three monsoon months being exceptions), and is often as low as 20-40 per cent. The rainfall is relatively small. Before the twentieth century, the concentrations of the corroding CO₂ in the atmosphere were low. There has been more corrosion-passivating ammonia in the atmosphere on account of the biological waste products in the neighbourhood areas.