the treatment of chitosan or preferably an aqueous solution of a chitosan salt with an appropriate halogenating agent results in the conversion of some to essentially all of the 2 - deoxy - 2 - aminoglucose monomeric units present in chitosan to 2 - mono or 2 , 2 - dihalo aminoglucose monomeric units to yield a novel polymeric composition having superior flocculating properties . the term halogenating agent is used in the conventional sense of being those agents having halogen bound to a strongly electronegative atom such as oxygen , nitrogen , or another halogen , and capable of donating a positively charged halogen atom . suitable halogenating agents include sodium hypochlorite , calcium hypochlorite , chlorine , bromine , aqueous chlorine solutions , aqueous bromine solutions , n - chlorosuccinimide , sodium hypobromite , pyridinium bromide perbromide , n - bromosuccinimide , chloramine - t , and the like . other suitable halogenating agents will be readily apparent to those skilled in the art . sodium hypochlorite is preferred because of its ready availability and low cost . while n - halochitosans can be prepared by direct action of the halogenating agent on chitosan , the preferred mode is by action of the halogenating agent on an aqueous solution of a chitosan salt . in this manner , the halogenating agent is not concentrated at the surface of the solid polymer causing non - uniformity between the surface and the interior of the particle . when it is desired to isolate the n - halochitosan , the concentration of chitosan salt may be from about 0 . 1 to 5 . 0 % preferably from about 0 . 2 - 2 %. when it is desired to use the n - halochitosan as a flocculating aid , it is preferred to add 1 - 1000 ppm of the chitosan salt to the material to be flocculated and then adding the halogenating agent so that the n - halochitosan is formed in intimate contact with the flocculate to achieve maximum efficiency . the formation of n - halochitosans can be conducted at 0 ° to 80 ° c ., preferably at 15 °- 30 ° c . to optimize reaction rate and minimize decomposition of the product . the halogenating agent can be employed at levels of from about 0 to 3 stoichiometric equivalents of available halogen per equivalent of 2 - aminoglucose monomeric units in the chitosan . depending on the amount of halogenating agent employed , the degree of halogen substitution on the 2 - aminoglucose unit will vary from about 0 to 2 halogen atoms per 2 - aminoglucose unit . for flocculation applications , a degree of substitution of from about 0 . 3 to 1 . 8 is preferred . depending on the halogenating agent chosen , the reaction is generally complete in 1 - 60 minutes . when sodium hypochlorite is chosen , the reaction is very rapid and is complete in less than 10 minutes . less reactive halogenating agents such as n - bromosuccinimide may require 30 - 60 minutes or even longer depending on temperature . the n - halochitosan may be isolated from the reaction mixture by conventional techniques such as filtration or centrifugation . illustrative of the materials to be flocculated by the products of our invention there may be mentioned proteins , algae , carbohydrates , oils ( edible and hydrocarbon ), metallic oxides , poultry processing waste water and brewery sludge . in some instances , the n - halochitosans are able to produce results equivalent to those achieved with chitosan at a significantly lower rate of application . in other cases , notably oils , the n - halochitosans are able to induce flocculation in systems where chitosan is totally ineffective . the chitosan employed in this and subsequent examples was profloc ® f , obtained from protan , inc ., raymond , wash . it contained 28 % 2 - deoxy - 2 - acetamidoglucose and 72 % 2 - deoxy - 2 - aminogluccse monomeric units and was used without further purification . to 100 ml of water was added 1 . 0 g of chitosan and 1 . 0 g of glacial acetic acid to make a solution of chitosan acetate . to 22 . 6 ml of this solution at 20c . was added 6 . 26 g of commercial 5 % sodium hypochlorite . this corresponds to a ratio of two available chlorine atoms per equivalent of amino groups in the polymer . the mixture was stirred for 3 minutes and the n - chlorochitosan isolated by filtration . iodimetric titration with sodium thiosulfate revealed that the degree of substitution was 1 . 53 . this example illustrates the preparation of n - chlorochitosan from chitosan and chloramine - t and the enhanced performance of n - chlorochitosan over chitosan in flocculating an aqueous dispersion of peanut oil . a dispersion of peanut oil in water was prepared by mixing 4 . 0 g of peanut oil with 800 ml water for 5 minutes in a laboratory blender at 12 , 000 rpm . the dispersion was white and opaque and did not separate into distinct layers after standing undisturbed for 1 hour . the absorbance of this dispersion measured in a 1 . 0 cm cell at a wavelength of 660 nm was 1 . 610 when examined 0 . 5 hr after preparation . to 100 ml of freshly prepared peanut oil dispersion was added a solution of chitosan containing 1 . 0 mg / ml chitosan and 1 . 0 mg per ml acetic acid in the amounts described in table 1 which follows . in those cases where chloramine - t was employed , it was then added as a solution containing 5 . 7 μmole / ml in the amounts described in table 1 . the mixture was then allowed to stand undisturbed for 15 minutes and a sample withdrawn from the middle of the mixture for measurement of light absorbance as described above . results are summarized in the following table : table 1______________________________________ ml chitosan ml chloramine - trun no . solution solution absorbance______________________________________1 15 0 1 . 4962 14 14 0 . 2123 12 12 0 . 1644 10 0 1 . 4445 10 6 . 5 0 . 1866 10 13 . 0 0 . 023______________________________________ in the cases where chloroamine - t was employed , separation of layers began within 2 - 3 minutes . after 15 minutes , white semi - solid had separated to the top and clear , colorless liquid to the bottom as evidenced by the low light absorbance . when chloramine - t was not employed , the entire mixture remained uniform and opaque . this example illustrates the preparation of n - chlorochitosan from chitosan and n - chlorosuccinimide . separate solutions were prepared by dissolving 1 . 0 g chitosan ( 4 . 03 m mole nh 2 ) in ml of 1 % acetic acid solution and by dissolving 0 . 76 ( 5 . 7 m mole ) of n - chlorosuccinimide in 76 ml of water . these clear solutions were mixed together and stirred at 22 ° c . after 3 - 4 minutes a cloudy appearance developed and after 30 minutes the entire mixture was semi - solid . after 80 minutes , the gel was broken up mechanically , allowing a liquid phase to separate and the gel collected by filtration and washed with three 100 ml portions of water . analyses by iodometric titration revealed that the gel contained 3 . 21 m mole chloramine , equivalent to conversion of 80 % of the 2 - aminoglucose units to 2 - chloroaminoglucose units . this example illustrates the preparation of n - bromochitosan from chitosan and an aqueous solution of bromine . a solution containing 0 . 223 m mole / ml of bromine was prepared by dissolving about 4 g of bromine in 100 ml of 0 . 1n naoh . a second solution was prepared by dissolving 1 . 0 g of chitosan in 100 ml of 1 % acetic acid solution . to 45 . 8 ml of the chitosan - containing solution ( 1 . 85 m mole nh 2 ) was added 16 . 56 ml of the bromine solution and the mixture stirred for 45 minutes at 22 ° c . the solid was separated by filtration and washed with water . iodometric titration of the solid revealed the presence of 0 . 56 m mole of bromamine , equivalent to conversion of 30 % of the 2 - aminoglucose monomeric units to 2 - bromoaminoglucose . this example illustrates the enhanced performance of n - chlorochitosan over chitosan in flocculating a dispersion of crude oil . the oil dispersion was prepared by mixing 4 . 0 g of crude oil with 800 ml of water in a laboratory blender at 12 , 000 rpm for 5 minutes . it was black in color and completely opaque so that the absorbance of light of 660 nm wavelength was infinite when measured in a 1 cm cell . the dispersion was stable and did not separate into distinct layers even after standing undisturbed for 4 hours . to 100 ml of this dispersion was added a solution containing 1 . 0 mg / ml chitosan and 1 . 0 mg / ml acetic acid in the amounts indicated in table 2 . after mixing , a solution containing 4 . 3 μ mole / ml sodium hypochlorite was added in the amounts indicated in table 2 and the solution allowed to stand undisturbed for 15 minutes . in the cases where chitosan alone was employed , there was no visible change . in the cases where n - chlorochitosan was generated in situ from chitosan and sodium hypochlorite , separation of phases began within minutes . black , oily semi - solid rose to the top leaving clear , colorless liquid below . after 15 minutes , samples were withdrawn from the middle of the mixture and the absorbance of light of 660 nm wavelength measured in a 1 cm cell . the results are summarized in table 2 , illustrating the enhanced flocculation of crude oil with n - chlorochitosan . table 2______________________________________ ml sodium ml chitosan hypochlorite absorbancerun no . solution solution 660 nm______________________________________1 15 02 10 03 5 04 10 10 . 0275 7 7 . 042______________________________________ when higher proportions of chitosan and sodium hypochlorite to crude oil were employed , the sedimented layer became more rigid . at a ratio of 20 mg chitosan to 86 μ mole naocl to 100 ml of oil dispersion , the oil separated as spheres of 2 mm diameter that were solidified and could be separated from the liquid by conventional liquid - solid separation techniques such as filtration . this example illustrates the enhanced performance of n - chlorochitosan over chitosan in the flocculation of algae . a sample of pond water containing several species of algae was collected at moores lake , dover , del . the turbidity as measured by standard nephelometric techniques was 9 . 2 ntu . to 50 ml of this water was added a solution containing 0 . 5 mg / ml chitosan and 0 . 5 mg / ml acetic acid in the amounts indicated in table 3 . after mixing for 1 minute , a solution containing 2 . 15 μ mole / ml sodium hypochlorite was added in the amounts indicated in table 3 . the mixture was allowed to stand undisturbed for 15 minutes and samples withdrawn from the middle of the mixture for measurement of turbidity . when chitosan alone was employed , some of the algae flocculated and settled to the bottom , but much remained suspended giving the water a distinct green color . when n - chlorochitosan was generated in situ from chitosan and sodium hypochlorite , essentially all of the algae was sedimented leaving colorless water above the sediment . table 3______________________________________ ml chitosan ml nao clrun no . solution solution turbicity , ntu______________________________________1 2 0 6 . 02 3 0 6 . 03 2 2 1 . 04 2 3 1 . 8______________________________________