In a process of purifying a fluid such as water or an aqueous solution, the fluid, containing less than about 20 parts per million of ionizable solids to be removed, is treated with a hydrogen activated cation active material and then with an anion active material which has been treated or buffered with a reagent which brings the pH value of the effluent fluid to any desired point, for example, to about 7.5 if a substantially neutral effluent is desired. The reagent may consist, for example, of carbondioxide, or an aqueous solution of a mixture of an alkali metal carbonate and an alkali metal bicarbonate. The untreated fluid may be first passed through a cation and an anion active bed, or a series of alternate cation and anion active beds, to bring the content of ionizable solids to less than 20 parts in a million before it passes through the fluid cation active bed and buffered anion active bed. In an example, water is purified by passage through four columns packed alternately with cation and anion active resins, the former being pretreated with a solution of an acid or a salt of an alkali metal, and the latter with a dilute alkali solution. The final bed of anion active material is then further treated so that it maintains the pH value of the effluent at about 7.5, for example, by passing carbon dioxide through the water-filled bed, or by treating it with a dilute solution of sodium bicarbonate and a base such as sodium hydroxide or sodium carbonate. During the run, the pH value of the effluent drops very slowly to about 7, when a rapid fall occurs, indicating that the beds need reactivation. A similar process is described for the purification of 50 per cent glucose and sugar solutions, coloration of the effluent being avoided by treatment of the solution with decolourizing material such as charcoal or bone black. Examples of sugars which may be treated are maple invert, malt, or milk sugars, dextrose, fructose and natural and synthetic saccharides. The solutions are usually treated at temperatures from about 40 DEG C. to 8 DEG C. The method may be applied to the purification of aqueous solutions of gums, water-soluble proteins (for example, egg albumen, blood serum, gelatin, &c.) urea apple pectin, corn syrup, dyes, acrylonitrile, ethylene, cyanohydrin, alcohols (for example, methanol, ethanol, n-propanol, isopropanol, butanols, benzyl alcohol, ethylene glycol, glycerine and the monoalkyl ethers of ethylene or diethylene glycol). Esters such as ethyl and methyl acetate, glycol mono-acetate, triacetate, ethyl citrate, ethyl gluconate, methyl mucate, ethyl hydracrylate, ethyl glycolate, methyl glycerinate, may also be treated. Solutions of amino acids, such as glycine, alpha and beta alanine, guanadine acetic acid, glycocyamine, creatine and creatinine may be purified and brought to their isoelectric point by suitable selection of the buffering reagent in the final bed of anion active material. On purifying soluble organic acids, such as citric acid, alpha-hydroxy isobutyric acid, lactic acid, tartaric acid and acetic acid, the final bed of anion active material is buffered by an acidic reagent, such as carbonic acid, which is as highly or more highly ionized than the acid being purified. Aqueous solutions of formaldehyde may be purified and synthetic formaldehyde obtained by the oxidation of hydrocarbons may be given the same characteristics as that obtained from methanol by buffering the final bed by an acidic reagent to produce the desired pH value. Examples of suitable anion and cation active resins are given, including anion active resins which may be prepared from guanidine, guanyl urea, and biguanide in the manner described in Specifications 561,896 and 562,402. A method of preparing a suitable cation active resin is described, in which acetone and furfural are reacted in the presence of sodium hydroxide, the pH value being then brought to about 7 by the addition of dilute sulphuric acid. Sodium metabisulphite is added and after the exothermic reaction has subsided the mixture is refluxed and cooled, after which sulphuric acid furfural are added. The resulting solution is gelled in moulds, the gel being then granulated and heated. Specification 569,660, [Group I], also is referred to.ALSO:Aqueous solutions of gums, water-soluble proteins (e.g. egg albumen, blood serum and gelatine) and apple pectin, containing less than about 20 parts per million of ionizable solids to be removed, are purified by treating with a hydrogen activated cation active material and then with an anion active material which has been treated or buffered with a reagent which brings the pH value of the effluent fluid to any desired point, for example, to about 7.5 if a substantially neutral effluent is desired. The reagent may consist of carbon dioxide or an aqueous solution of a mixture of an alkali metal carbonate and an alkali metal bicarbonate. The untreated fluid may be first passed through a cation and an anion active bed, or a series of alternate cation and anion active beds, to bring the content of ionizable solids to less than 20 parts per million before it passes through the final cation active bed and buffered anion active bed. Examples of suitable anion and cation active resins are given (see Group I). Specifications 561,896, 562,402, [both in Group IV], and 569,660, [Group I], are referred to.ALSO:In a process of purifying a fluid such as water or an aqueous solution, the fluid, containing less than about 20 parts per million of ionizable solids to be removed, is treated with a hydrogen activated cation active material and then with an anion active material which has been treated or buffered with a reagent which brings the pH value of the effluent fluid to any desired point, for example to about 7.5 if a substantially neutral effluent is desired. The reagent may consist, for example, of carbon dioxide, or an aqueous solution of a mixture of an alkali metal carbonate and an alkali metal bicarbonate. The untreated fluid may be first passed through a cation and an anion active bed, or a series of alternate cation and anion active beds, to bring the content of ionizable solids to less than 20 parts in a million before it passes through the final cation active bed and buffered anion active bed. In an example, water is purified by passage through four columns packed alternately with cation and anion active resins, the former being pretreated with a solution of an acid or a salt of an alkali metal, and the latter with a dilute alkali solution. The final bed of anion active material is then further treated so that it maintains the pH value of the effluent at about 7.5, for example by passing carbon dioxide through the water-filled bed, or by treating it with a dilute solution of sodium bicarbonate and a base such as sodium hydroxide or sodium carbonate. During the run of the pH value of the effluent drops very slowly to about 7, when a rapid fall occurs, indicating that the beds need reactivation. A similar process is described for the purification of 50 per cent. glucose and sugar solutions, coloration of the effluent being avoided by treatment of the solution with decolourizing material such as charcoal or bone black. Examples of sugars which may be treated are maple, invert, malt, and milk sugars, dextrose, fructose, and natural and synthetic saccharides. The solutions are usually treated at temperatures from about 40 DEG C. to 80 DEG C. The method may be applied to the purification of aqueous solutions of gums, water-soluble proteins (for example, egg albumen, blood serum, gelatine, &c.), urea, apple pectin, corn syrup, dyes, acrylonitrile, ethylene, cyanohydrin, alcohols (for example, methanol, ethanol, n-propanal, isopropanol, butanols, benzyl alcohol, ethylene, glycol, glycerine, and the monol-alkyl ethers of ethylene or diethylene glycol). Esters such as ethyl and methyl oxalate, glycol monoacetate, triacetate, ethyl citrate, ethyl gluconate, methyl mucate, ethyl hydro acrylate, ethyl glycolate, methyl glycerinate, may also be treated. Solutions of amino acids, such as glycine ,alpha and beta alanine, guanadine acetic acid, glycocyamine, creatine, and creatinine may be purified and brought to their isoelectric point by suitable selection of the buffering reagent in the final bed of anion active material. In purifying soluble organic acids, such as citric acid, alpha hydroxy, isobutyric acid, lactic acid, tartaric acid, and acetic acid, the final bed of anion active material is buffered by an acidic reagent such as carbonic acid, which is as highly or more highly ionized than the acid being purified. Aqueous solutions of formaldehyde may be purified, and synthetic formaldehyde obtained by the oxidation of hydrocarbons may be given the same characteristics as that obtained from methanol by buffering the final bed of an acidic reagent to produce the desired pH value. Examples of suitable anion and cation active resins are given, including anion active resins which may be prepared from guanidine, guanyl urea, and biguanide in the manner described in Specifications 561,896 and 562,402, [both in Group IV]. A method of preparing a suitable cation active resin is described, in which acetone and furfural are reacted in the presence of sodium hydroxide, the pH value being then brought to about 7 by the addition of dilute sulphuric acid. Sodium metabisulphite is added and after the exothermic reaction has subsided the mixture is refluxed and cooled, after which sulphuric acid and furfural are added. The resulting solution is gelled in moulds, the gel being then granulated and heated. Specification 569,660, [Group I], also is referred to.