We are using furnace oil for heating and drying aggregates in Hot mix plants(India) and how to test the purity of Fo on site quickly?
It depends upon the nature of the undesired materials:
Simple. Burn a small, measured quantity to heat a known quantity of water and measure the temperature rise of the water.
You just need a metal container to burn the oil, a beaker for the water and a thermometer. Any unburned impurities will remain in the container.