well as density and related to the viscosity of vegetable oils are known which implies that to see if oil can function as a lubricant simply knowing its density, so our present study we do the measurement of the density of two oils ( rapeseed and nigella ), and the results showed that rapeseed density decreases very dramatically depending on the temperature increase unlike the nigella , and we know very well that the oil nigella and expensive compared to rapeseed oil so we can not consider nigella oil as a good lubricant.
