An adduct of a hydrophilic inorganic solid, e.g. clay, silica or alumina, in a form having a large surface area (e.g. at least 10 sq. m/gm.), with an organic isocyanate or isothiocyanate may be obtained by (a) suspending the solid in an inorganic liquid containing said organic substance, heating, preferably under reflux and recovering the adduct by filtering or centrifuging; or (b) suspending the solid in e.g. 1 to 5 parts by weight of an organic liquid and refluxing to remove water azeotropically, introducing said organic substance and heating, preferably under reflux, e.g. for 1 to 10 hours at 50 DEG C. up to 150 DEG C.; or (c) introducing the solid in substantially dry form and the organic substance into a pressure vessel, sealing the vessel and heating to a temperature at which an appreciable amount of the organic substance is present in the vapour phase, e.g. 100 DEG to 250 DEG C. from 1 to 5 hours; or (d) fluidizing the solid in an upward stream of gas whilst introducing vaporized isocyanate or isothiocyanate into the fluidized bed. A catalyst of the acid-base type, e.g. pyridine/acetic acid, may be used, especially with isothiocyanates. The adduct is generally less hydrophilic than the original inorganic solid, and may be hydrophobic, and in the form of a non-aggregated, finely divided powder. The product may be an adduct of a disubstituted urea formed by hydrolysis with water if present, or may be of urethane type. It is preferred to wash the adduct to destroy unreacted isocyanate present. Quantities of the organic substance to be used may be e.g. from 1 to over 100 per cent, generally 5 to 50 per cent by weight of the inorganic solid, or in the case of base exchanging clays an amount equivalent to once to twice the base exchange capacity is usually employed. The inorganic substance may be dried provided the surface area is not reduced, e.g. clay may be dried at up to 500 DEG C. Specified inorganic solids which may be treated are: clays (which may be purified, e.g. by settling in water): montmorillonites, e.g. sodium and calcium bentonites and magnesium-substituted montmorillonite, beidellite, attapulgite, nontronite, saponite, kaolinite, hectorite, acid clays (either natural or produced by treating sodium or calcium bentonite with aqueous acid); natural and artificial silicates of di- and trivalent metals, e.g. aluminium, magnesium, iron and calcium; diatomaceous earth, mica, asbestos, silica; metal oxides and hydroxides, e.g. aluminas and aluminium hydroxides, iron hydroxide, molybdenum, zinc and vanadium oxides, oxides and hydroxides of alkaline earth metals, carbonates such as calcium carbonate; phosphates, sulphates and sulphides of heavy metals, e.g. molybdenum sulphide. Examples specify montmorillonite-containing clays, bentonite, hectorite, "Super-Filtrol" (an acid-activated montmorillonite), and "Filtrol" (Registered Trade Mark), asbestos, aluminium hydroxide, hydrated alumina and silica gel. The following classes of isocyanates are specified, and it is stated that the corresponding isothiocyanates may be used: aliphatic (alkyl or alkenyl, straight or branched chain), alicyclic (cycloparaffinic or cyclo-olefinic), aryl, i.e. directly attached to e.g. benzene or naphthalene nuclei, heterocyclic nuclei such as furane, and combinations (alkaryl; aralkyl, e.g. benzyl; aliphatic, alicyclic or aryl-substituted heterocyclic nuclei, the isocyanate group being attached to the non-heterocyclic portion). These classes may be unsubstituted or non-functionally substituted, e.g. with chloro-, nitro- or bromo-groups. Specified compounds are ethyl isocyanate, phenyl isocyanate, octadecyl isocyanate, alpha-naphthyl isocyanate, 2.4 - diisocyanato - toluene, benzyl isocyanate, the toluene isocyanates, p.p1-diisocyanato diphenylmethane, octyl isocyanate, n-butyl isocyanate, isobutyl isocyanate, sec. butyl isocyanate, tert. butyl isocyanate, 1.8-diisocyanato-n-octane, the cyclohexenyl isocyanates, the isocyanatofuranes, the butenyl isocyanates, 4.41.411 - triphenylmethane triisocyanate, 2-butene - 1.4 - diisocyanate, meta - xylenealpha.alpha1 - diisocyanate, cyclohexane - 1.4-diisocyanate, 2 - picoline - alpha - isocyanate, 3 - chloro -, 3 - nitro -, 3 - bromo - propyl isocyanates, and in the examples, octadecyl isocyanate, 2.4 - diisocyanato toluene, and phenyl isocyanate are used. A mixture of octadecyl isocyanate with 2-butene-1.4-diisocyanate and of octadecyl isocyanate with p.p1-diisothiocyanato diphenylmethane or of ethyl isocyanate with octadecylisothiocyanate may also be used, and a substance containing both isocyanate and isothiocyanate groups can also be used. When using techniques (a) or (b) suitable solvents are: hydrocarbons; aryl, alicyclic, or aliphatic benzene, toluene, xylene (these are exemplified), cumene, cyclohexylbenzene, cyclohexane, dimethyl pentane, octane, dodecane, naphthas (boiling point 50 DEG to 150 DEG C.), olefines and cycloolefines; non-functionally substituted hydrocarbons, ethers, nitro- and halogenohydrocarbons, e.g. n-propyl ether, isopropyl ether, methyl hexyl ether, dibromobutane, ethylene dichloride, carbon tetrachloride, nitrobenzene, nitrobutane. Alcohols, carboxylic acids, esters and amines should be avoided. The products may be washed e.g. with water followed by methanol, ethanol, hydrocarbons such as benzene and hexane, followed by lower dialkyl others, e.g. ethyl ether. Specifications 756,966, [Group III], and 795,052 are referred to.ALSO:An adduct of a hydrophilic inorganic solid, e.g. clay, silica or alumina, in a form having a large surface area (e.g. at least 10 sq. m./gm.), with an organic isocyanate or isothiocyanate, may be obtained by (a) suspending the solid in an inorganic liquid containing said organic substance, heating, preferably under reflux and recovering the adduct by filtering or centrifuging or (b) suspending the solid in, e.g., 1 to 5 parts by weight of an organic liquid and refluxing to remove water azeotropically, introducing said organic substance and heating, preferably under reflux, e.g. for 1 to 10 hours at 50 DEG C. up to 150 DEG C.; or (c) introducing the solid in substantially dry form and the organic substance into a pressure vessel, sealing the vessel and heating to a temperature at which an appreciable amount of the organic substance is present in the vapour phase, e.g. 100 DEG to 250 DEG C. from 1 to 5 hours; or (d) fluidizing the solid in an upward stream of gas whilst introducing vaporized isocyanate or isothiocyanate into the fluidized bed. A catalyst of the acid-base type, e.g. pyridine/acetic acid, may be used, especially with isothiocyanates. The adduct is generally less hydrophilic than the original inorganic solid, and may be hydrophobic, and in the form of a nonaggregated, finely-divided powder. The product may be an adduct of a di-substituted urea formed by hydrolysis with water if present, or may be of urethane type. It is preferred to wash the adduct to destroy unreacted isocyanate present. Quantities of the organic substance to be used may be, e.g., from 1 to over 100 per cent, generally 5 to 50 per cent by weight of the inorganic solid, or in the case of base exchanging clays an amount equivalent to once to twice the base exchange capacity is usually employed. The inorganic substance may be dried provided the surface area is not reduced, e.g. clay may be dried at up to 500 DEG C. Specified inorganic solids which may be treated are:-clays (which may be purified, e.g. by settling in water): montmorillonites, e.g. sodium and calcium bentonites and magnesium-substituted montmorillonite, beidellite, attapulgite, nontronite, saponite, kaolinite, hectorite, acid clays (either natural or produced by treating sodium or calcium bentonite with aqueous acid); natural and artificial silicates of di- and trivalent metals, e.g. aluminium, magnesium, iron and calcium; diatomaceous earth, mica, asbestos, silica; metal oxides and hydroxides, e.g. aluminas and aluminium hydroxides, iron hydroxide, molybdenum, zinc and vanadium oxides, oxides and hydroxides of alkaline earth metals, carbonates such as calcium carbonate; phosphates, sulphates and sulphides of heavy metals, e.g. molybdenum sulphide. Examples specify montmorillonite-containing clays, bentonite, hectorite, "Super-Filtrol" (an acidactivated montmorillonite), and "Filtrol" (Registered Trade Mark), asbestos, aluminium hydroxide, hydrated alumina and silica gel. The following classes of isocyanates are specified, and it is stated that the corresponding isothiocyanates may be used:-aliphatic (alkyl or alkenyl, straight or branched chain), alicyclic (cycloparaffinic or cyclo-olefinic), aryl, i.e. directly attached to, e.g., benzene or naphthalene nuclei, heterocyclic nuclei such as furane, and combinations (alkaryl; aralkyl, e.g. benzyl; aliphatic, alicyclic or aryl-substituted heterocyclic nuclei, the isocyanate group being attached to the non-heterocyclic portion). These classes may be unsubstituted or nonfunctionally substituted, e.g. with chloro-, nitro- or bromo-groups. Specified compounds are ethyl isocyanate, phenyl isocyanate, octadecyl isocyanate, alpha-naphthyl isocyanate, 2,4-diisocyanato-toluene, benzyl isocyanate, the toluene isocyanates, p,p1-diisocyanato diphenylmethane, octyl isocyanate, n-butyl isocyanate, isobutyl isocyanate, sec.-butyl isocyanate, tert.-butyl isocyanate, 1,8-diisocyanato-n-octane, the cyclohexenyl isocyanates, the isocyanatofuranes, the butenyl isocyanates, 4,41,411-triphenylmethane triisocyanate, 2-butene-1,4-diisocyanate, meta - xylene - alpha, alpha1 - diisocyanate, cyclohexane - 1,4 - diisocyanate, 2 - picoline-alpha-isocyanate, 3-chloro-, 3-nitro-, 3-bromo-propyl isocyanates, and in the examples, octadecyl isocyanate, 2,4-diisocyanato toluene, and phenyl isocyanate are used. A mixture of octadecyl isocyanate with 2-butene-1,4-diisocyanate and