Polarised light micrograph of crystals of DDT (dichlorodiphenyltrichloroethane) and salicyclic acid. DDT is a pesticide which was widely used in the 1940s & 1950s. It was later found to be dangerous and restrictions are now placed on its use. Salicyclic acid is a naturally occurring carboxylic acid found in certain plants. It is used in making aspirin and in the food and dyestuff industries. Magnification: x60 at 35mm size.