of limitation in the exhaust path of an internal combustion engine in the flue or smoke stack of an industrial plant and at the input or output of an air conditioning unit or the like when so used the filter is highly efficient in removing unwanted gaseous and particulate pollutants the filter will be described in connection with its use as a cigarette filter however its use as a filtering medium for other applications should be borne in mind at all times the invention is based on the oxidization of cellulose with nitric acid in which the nitric acid oxidizes the primary hydroxyl group to carboxyl without affecting the rest of the molecule appreciably except for a considerable reduction in chain length cellulose comprises at least one third of all vegetable matter cotton and wood the principal sources of industrial cellulose are about 90 and 50 cellulose respectively the preferred source of cellulose for this invention is chemical cotton which comprises cotton linters which are the short fibers removed from cotton seeds after the long fibers have been taken off by ginning for use in textiles the cotton linters are purified by pressure digestion at 130 u00b0 c to 180 u00b0 c with a solution containing 2 to 5 sodium hydroxide and by a subsequent bleaching to remove color bodies chemical cotton contains about 99 alpha cellulose raw cotton which typically contains less than 10 of non cellulisic impurities such as proteins.