Mero-aryl formazane dyestuffs, metallized or not metallized, are prepared by double coupling with two molecules of a diazonium salt or by two successive couplings with two similar or different diazonium salts, of substituted or unsubstituted aromatic amines, on a coupling component of formula:- <FORM:0768662/IV(c)/1> where Ar is a substituted or unsubstituted aryl radical and X and Y are electron-attracting groups (i.e. the groups -CN and -COZ wherein Z is -OH, -NH2, H or an alkyl, aryl, alkoxy or esterified carboxylic radical) either both being sufficiently labile to be simultaneously substituted by the diazonium salt, or one of which (X) is labile, permitting a first coupling and the other (Y) becoming labile after saponification thus permitting a second coupling; the double coupling or the second coupling being carried out in the presence of a metal salt (i.e. copper or nickel salt) if the metallized complexes are desired. Specified coupling components are phenyl - formyl - acetic acid, alpha - phenyl - acetoacetic - acid, phenyl - cyanacetic acid, ethyl phenyl - formyl - acetate, methyl m - tolylformyl acetate, ethyl alpha - naphthyl - formyl acetate, ethyl alpha - phenyl acetoformyl acetate, ethyl alpha - phenyl acetoacetate, diethyl phenyloxalacetate, ethyl phenylcyanacetate, phenyl cyanacetamide, phenyl - formyl - acetonitrile, alpha - phenyl - acetoacetonitrile, ethyl phenyl - ayan pyruvate, o phenyl - o - cyanacetophenone, and a compound in which X and Y form part of a cyclic system, i.e. 2-phenyl - indane - dione - 1:3. The product of the first of two successive couplings is a hydrazone of formula:- R1-NH-N=C (Ar)-Y wherein R1 is the radical of the aromatic amine used, which may be isolated (see Group IV(b)). The second coupling which may be preceded by saponification of Y gives the formazane of formula:-R1-NH-N=C(Ar)-N=N-R2, R2 being the radical of the second aromatic amine used. When the amine radicals R1 and R2 are orthohydroxylated the metal complexes may be formed and dye wool, silk and nylon in green, blue, red and brown shades. In examples: (1) alpha - phenyl - acetoacetonitrile is coupled successively with the diazo compounds from aniline and 2 - nitro - 4 - chloro - aniline after intermediate saponification to give N - phenyl - N1 - (21-nitro - 41 - chlorophenyl) - ms - phenyl - formazane; (2) 2 - phenyl - indane - dione - 1:3 is coupled as in (1) with the diazo compounds from sulphanilic acid and 5 - nitro-2 - amino - anisole to give N - (4 - sulphophenyl) - N1 - (21 - methoxy - 41 - nitrophenyl - ms - phenyl - formazane; (3) alpha - phenyl - acetoacetic acid is coupled with the diazo compound from 4 - sulpho - 2 - aminophenol to give N:N1 - di(2 - hydroxy - 5 - sulphophenyl) - ms - phenyl - formazane which gives a blue after-coppered dyeing on wool fibres and forms a copper complex in ammoniacal medium; (4) ethyl alpha - phenyl - acetoacetate is coupled with the diazo compound from 4 - sulpho - 6 - nitro - 2 - aminophenol the intermediate hydrazone is saponified with caustic soda and coupled with the diazo compound from 4 - nitro - 6 - chloro - 2 - aminophenol in the presence of copper sulphate to give the copper complex of N - 2-hydroxy - 3 - nitro - 5 - sulphophenyl) - N1 - (21 - hydroxy - 31 - chloro - 51 - nitrophenyl) - ms - phenyl - formazane; (5) methyl m -tolyl - formyl acetate is coupled as in (4) with the diazo compounds from 4 - sulpho - 6 - nitro - 2 - aminophenol and 4 - nitro - 2 - aminophenol to give the copper complex of N - (2 - hydroxy - 3 - nitro-5 - sulphophenyl) - N1 - (21 - hydroxy - 51 - nitrophenyl) - ms - m - tolyl - formazane; (6) ethyl alpha - phenyl - formyl acetate is coupled, as in (4) but using nickel sulphate in the second coupling, with the diazo compounds from picramic acid and 4 - sulpho - 2 - aminophenol to give the nickel complex of N - (2 - hydroxy - 3:5 - dinitrophenyl) - N1 - (21 - hydroxy - 51 - sulphophenyl) - ms - phenyl formazane; (7) diethyl phenyl - oxalacetate is coupled as in (4) with the diazo compounds from 4 - sulpho - 6 - nitro - 2 - aminophenol and picramic acid to give the copper complex of N - (2 - hydroxy - 3 - nitro - 5 - sulphophenyl) - N1 - (21 - hydroxy - 31:51 - dinitrophenyl) - ms - phenyl formazane; (9) ethyl alpha - phenyl - formyl acetate is coupled as in (6) with the diazo compounds from 4:6 - dinitro - 2 - aminophenol and 1 - amino - 4 - sulpho - 6 - nitro - naphthol (2) to give the nickel complex of N - (2 - hydroxy - 3:5 - dinitrophenyl) - N1 - (21 - hydroxy - 41 - sulpho - 61 - nitro - naphthyl (11)) - ms - phenyl formazane; (10) as in (9) but coupling with the diazonium compounds from 4:6 - dinitro - 2 - aminophenol and 2 - amino - 4 - nitro - 7 - sulpho - naphthol (1) to give the nickel complex of N - (2 - hydroxy - 3:5 - dinitrophenyl) - N1 - (N1 - hydroxy - 41 - nitro - 71 - sulphonaphthyl (21)) - ms - phenyl formazane; (11) ethyl alpha - phenyl - formyl acetate is coupled as in (4) with the diazo compounds from 4 - nitro - 6 - chloro - 2 - aminophenol and 4 - sulpho - 6 - nitro - 1 - amino - 2 - naphthol to give the copper complex of N - (2 - hydroxy - 3 - chloro - 5 - nitrophenyl) - N1 - (21 - hydroxy - 41 - sulph - 61 - nitro - naphthyl (11)) - ms - phenyl formazane; (12) ethyl alpha - (1 - naphthyl) - formyl acetate is coupled as in (4) with the diazo compound from 4 - sulpho - 6 - nitro - 2 - aminophenol and 4 - nitro - 2 - aminophenol to give the copper complex of N - (2 - hydroxy - 3 - nitro - 5 - sulphophenyl) - N1 - (21 - hydroxy - 51 - nitrophenyl) - ms - (1 - naphthyl) - formazane; (13) methyl 4 - chlorophenyl - formyl acetate is coupled with the diazo compound from 4 - nitro - 6 - sulpho - 2 - aminophenol, saponified and again coupled with the same diazo compound in the presence of N:N - di - (2 - hydroxy - 3 - sulpho - 5 - nitro - phenyl) - ms - 4 - chlorophenyl-formazane.ALSO:Aqueous liquors containing suspended negatively charged particles which are in a flocculated condition by virtue of the presence of inorganic cations in amount sufficient to neutralize the charges of the particles, are treated with an anionic polyelectroylte which is a water soluble linear polymer or co-polymer containing free carboxyl groups or carboxyl groups which have been neutralized and are in salt form, in an amount not more than 0.1 per cent based on the liquor to be treated whereby the particles become aggregated and separable from the liquid phase. The process is applicable to natural or industrial waters for example surface or sub-surface waters, industrial effluents, water in fish ponds or lakes and also to the treatment and recovery of clays and the production of paper, for example, the application of fillers to paper pulp and to the recovery of pigments from aqueous suspension thereof. The anionic polyelectrolytes are preferably polymerization products of a b ethylenically unsaturated aliphatic carboxylic acids or salts of such polymerization products for example homopolymers of the acrylic acid series and copolymers of the acrylic series with polymerizable olefinic compounds for example styrene, vinyl formate, acetate, chloride or methyl ether. Specified anionic polyelectrolytes the preparation of which is given (see Group IV(b)) are: Monosodium salt of vinyl acetate-maleic anhydride copolymer, diammonium salt of vinyl acetate-maleic anhydride copolymer, ammonium salt of vinyl acetate-maleamic acid copolymer, sodium salt of vinyl alcohol-maleic acid copolymer, diammonium salt of vinyl methyl ether-maleic anhydride copolymer, diammonium salt of vinyl ethyl ether-maleic anhydride copolymer, diammonium salt of isobutylene-maleic anhydride copolymer, diammonium salt of styrene-maleic anhydride copolymer, diammonium salt of ethyl acrylatemaleic anhydride copolymer, monocalcium salt of vinyl acetate-maleic anhydride copolymer, diammonium salt of vinyl acetate-maleic anhydride copolymer, diammonium salt of isopropenyl acetatemaleic anhydride copolymer, diammonium salt of vinyl isopropyl ether-maleic anhydride copolymer, diammonium salt of vinyl n-butyl ether-maleic anhydride copolymer, diammonium salt of vinyl chloride-maleic anhydride copolymer, diammonium salt of vinyl chloroacetatemaleic anhydride copolymer, ammonium salt of terpolymer of vinyl acetate-maleic anhydride-methyl acid maleate, monocalcium salt of vinyl methyl ether-maleic anhydride copolymer, sodium salt of a copolymer of acrylic acid and vinyl alcohol, sodium polymethacrylate, ammonium polymethacrylate, ammonium polyacrylate, sodium polyacrylate, ammonium salt of a polyacid obtained by acid hydrolysis of methacrylic acid (50 per cent)-acrylonitrile (50 per cent) copolymer, diammonium salt of vinyl methyl or ethyl ether-maleic anhydride copolymer. The molecular weight of anionic polyelectrolyte employed should normally be in excess of 5000 and desirably in the range of 3000-100,000 and they are suitably employed in amounts greater than 5 micro-normal units per litre. The polyelectrolyte should be uniformly distributed in the liquors by agitation. According to examples (1) aluminium sulphate solution prepared by reacting calcined clay with 42 to 48 per cent sulphuric acid followed by dilution with water to dissolve the aluminium sulphate, is clarified by the addition of the monosodium salt of vinyl acetate maleic anhydride copolymer. The aluminium sulphate may be recovered by evaporation and crystallization. (2) An aqueous clay slurry containing 40 per cent of solid particles in a flocculated condition due to the presence of inorganic cations was treated with ammonium polyacrylate with stirring whereby the clay particles aggregated and a filterable slurry resulted. The quantity of polyelectrolyte was 1000 micro-normal units per litre which is equivalent to 0.25 pounds per 1,000 pounds of clay. (3) A suspension of silt loam in water was treated with the amonium salt of a vinyl