Particles ??? solid, hydrophilic material are coated firstly by phase separation of a material presenting a lipophilic surface from a non-aqueous medium and subsequently adding a second coating by phase separation of a material presenting a hydrophilic surface from an aqueous medium.  Suitable materials for the first coat are linear macromolecular synthetic polymers whose structure comprises both lipophilic and hydrophilic units, e.g. hydrolysed styrene-maleic acid copolymers; polyamides, polybasic polymers, e.g. deacetylated chitin, polyvinyl pyridine, polymeric ammonium salts and derivitives of naturally occurring polymers, e.g. ethyl and benzyl cellulose, cellulose acetate, di- and tri-nitrocellulose, carbohydrate acetate phthalates and phospholipids, e.g. lecithins.  The second coating may comprise gelatin, alginates, pectins or casein, two or more hydrophilic colloids at least one of which is gelable and at least one of which is opposite in charge from the others of the system and linear macromolecular synthetic polymers of the types referred to above.  For the first coat, phase separation may be achieved by addition to a suspension of the material to be coated in a solution of the coating material of a miscible liquid which is a non-solvent for the coating material.  For the second coat, it may be achieved by addition of an electrolyte, of a liquid having a low solubility for the colloid or by adjustment of the pH.  Either or both coats may be hardened by chemical or physical means and the product may be washed and dried.  Specific examples include amaranth coated firstly with cellulose acetate butyrate and secondly with gelatin and dibasic calcium phosphate coated firstly with cellulose acetobutyrate and secondly with gelatin. Specifications 751,600, 929,225, 929,226 and 931,148 are referred to.ALSO:Particles of dicalcium phosphate are coated firstly with cellulose acetobutyrate and subsequently with gelatin by a two-stage phase separation process firstly from non-aqueous media and secondly from aqueous media (see Group VI) to give a material useful as a slow release fertilizer.  Specifications 751,600, 929,225, 929,226 and 931,148 are referred to.ALSO:Particles of liquid or solid hydrophilic material are coated firstly by phase separation of a material presenting a lipophilic surface from a non-aqueous medium and subsequently adding a second coating by phase separation of a material presenting a hydrophilic surface from an aqueous medium.  Suitable materials for the first (pre-) coat are synthetic polymers, e.g. linear macromolecular polymers whose structure comprises both lipophilic units, e.g. those derived from styrene or ethylene and derivatives thereof and hydrophilic units, e.g. those derived from unsaturated acids or amides.  Preferred polymers of this class are the hydrolysed styrenemaleic anhydride copolymers which may include minor amounts of other polymer units and may be represented by the general formula [-R-R1-]n, wherein R represents lipophilic polymer units of which more than 70% are styrene residues and R1 represents hydrophilic polymers of which more than 50% (preferably more than 70%) are maleic acid residues and n is an integer from about 90 to 1000.  Other suitable polymers include polyamides, polybasic polymers, e.g. deacetylated chitin, polyvinyl pyridine, polymeric quaternary ammonium salts and derivatives of naturally occurring polymers, e.g. ethyl cellulose, cellulose acetate, di- and tri-nitrocellulose, and carbohydrate acetate phthalates and phospholipids, e.g. lecithins. The second coating may comprise a gelable hydrophilic colloid, e.g. gelatine, alginates, pectins or casein; at least two hydrophilic colloids, at least one of which is gelable and at least one of which is opposite in charge from the others of the system; or a synthetic linear macromolecular polymer of the general type referred to above.  For the first coat, phase separation may be achieved by the addition, to a dispersion of the material to be coated in the polymer solution, of a liquid which is miscible with the polymer-solvent and which is a non-solvent for the polymer and the dispersed material.  For the second coat, phase separation may be by addition of an electrolyte, of a liquid having a low solubility for the colloid or by the adjustment of pH.  Either or both coats may be hardened by either chemical methods, e.g. treatment with formaldehyde, alums, tannic acid &c. or by physical means, e.g. desiccation or irradiation, and the final product may be washed and dried.  Specific examples include: (a) sodium (2,4-dichlorophenoxy) acetate with a benzyl cellulose pre-coat and an outer coating of gelatine (slow release weed-killer), (b) ascorbic acid with an ethyl cellulose pre-coat and an outer coat of styrene-maleic acid copolymer (suitable for suspension in aqueous vitamin preparations including those containing cyanocobalamin), (c) pancreatin with a styrenemaleic acid copolymer pre-coat and a gelatine/acacia coat (enteric medicament), and (d) methylscopolamine hydrobromide pre-coated with cellulose acetate butyrate and coated with styrene-maleic acid copolymer.  Specifications 751,600, 929,225, 929,226 and 931,148 are referred to.