The clouds consists of charged particles of water dispersed in air. Some of them are positively charged, others are negatively charged. When positively charged clouds come closer, they cause lightening and thundering whereas when positive and negative charged colloids come closer, they cause heavy rain by aggregation of minute particles. It is possible to cause artificial rain by throwing electrified sand or silver iodide from an aeroplane and thus, coagulation the mist hanging in air.
AgI helps in artificial rain because :