ABSTRACT
Filtration is the process of removing material from a substrate in which it is suspended. Filtration is accomplished by passing the mixture to be processed through one of the many available sieves, called filter media. There are two general methods of filtration: gravity and vacuum. Membrane filters are thin polymeric structures with extraordinarily fine pores. They are composed of pure, biologically inert cellulose esters or other polymeric materials. With proper filter selection, they yield a filtrate that is ultra clean and/or sterile. Membrane filters are available in a wide variety of pore sizes in a number of different materials. During gravity filtration, the filtrate passes through the filter medium under the forces of gravity and capillary attraction between the liquid and the funnel stem. Many substances cannot be distilled satisfactorily at atmospheric pressure because they are sensitive to heat. Vacuum distillation is a distillation under reduced pressure and it makes distillation possible at lower temperatures.
