Mixed ethers, in which one of the radicles attached to the ethereal oxygen atom is a tertiary alkyl group, are manufactured by reacting tertiary olefines with alcohols in the presence of condensation catalysts at temperatures below 150 DEG C., preferably below 100 DEG C. Instead of pure tertiary olefines there may be employed mixtures containing them, such as are obtained from natural gas by cracking, from gases or products formed in distilling or cracking petroleum or petroleum products, from peat, coal, oil shales and like carboniferous natural materials, or from the products formed by destructive hydrogenation of carbonaceous materials such as coal, brown coal, tar, coal tar, petroleum and petroleum products and other carbonaceous materials, such mixtures preferably being first fractionated by condensation, distillation or both, whereby hydrocarbons containing the same number of carbon atoms in the molecule are segregated into one fraction. In this case the reaction is carried out at temperatures below those at which secondary olefines are substantially attacked, the tertiary olefines being selectively absorbed. As alcohols may be employed primary or secondary aliphatic or aromatic alcohols, e.g. methyl, ethyl, n-propyl and isopropyl alcohols, also aliphatic polyhydric alcohols, e.g. ethylene glycol and its homologues such as propylene and butylene glycols, branched chain glycols, e.g. isobutylene glycol, glycerol, sorbitol, erythritol, pentaerythritol, mannitol, symmetrical or asymmetrical, straight or branched chain polyglycols, e.g. dipropylene, dibutylene, triethylene, ethylene-propylene, ethylene-butylene, propylene-butylene, isobutylene - isopropylene and isobutyleneethylene glycols, also ethers of aliphatic polyhydric alcohols containing at least one free hydroxyl group. As catalysts may be employed acids, e.g. sulphuric acid or the sulphonic acids of benzene and its homologues, or metallic chlorides, e.g. aluminium chloride. Other suitable catalysts when employing polyhydric alcohols are hydrochloric acid, acid salts, e.g. acid sulphates of alkali metals, and in certain cases known alkaline condensation catalysts. Any desired proportion of reagents may be employed according to whether the substantially complete removal of tertiary olefines or the substantially complete conversion of the alcohol is the object. The order of introduction of the reagents may be varied, e.g. the alcohol and catalyst may be added to the olefine or vice versa, or the alcohol and olefine to the catalyst or vice versa. The temperature employed depends on the concentration of the tertiary olefines, being preferably below 95 DEG C. when using pure tertiary olefines, but higher when employing tertiary olefines diluted with other hydrocarbons or inert fluids. The process in the case of polyhydric alcohols may be carried out at normal, elevated or reduced pressure, and at various temperatures, depending on the pressure employed and the quantity and character of the tertiary olefine, alcohol and catalyst used. The products from primary and secondary aliphatic alcohols may be used as such or mixed with other substances as diluting agents for solutions of lacquers and varnishes, e.g. for solutions of nitrocellulose in ethyl acetate, or as solvents and extracting agents for organic substances such as alkaloids, essential oils and essences. The products from aliphatic polyhydric alcohols or ethers thereof may be used as substitutes for polyhydric alcohols in dyeing, in the explosives industry, in the textile industry, as constituents of lubricants for machinery, for solvent or preparation purposes and as extraction agents for essential oils in the manufacture of flavours and perfumes. In certain cases their solutions may be used as cooling liquids for internal combustion engines. Those which are nitro-cellulose solvents of sufficiently high boiling point can be used as plasticizers for cellulose esters. Examples describe the preparation of: (1) isopropyl tertiary butyl ether from isopropyl alcohol and isobutylene in the presence of sulphuric acid; (2) methyl tertiary butyl ether from methyl alcohol and isobutylene in the presence of sulphuric acid; (3) as in (2) but employing a commercial butane-butene fraction; (4) as in (2) but working in the gaseous phase by passing a mixture of isobutylene and inert gas successively through two solutions of sulphuric acid in methyl alcohol; (5) the ether from trimethylethylene and methyl alcohol in the presence of sulphuric acid; (6) isobutyl tertiary butyl ether from isobutyl alcohol and isobutylene in the presence of sulphuric acid; (7) isoamyl tertiary butyl ether from isoamyl alcohol and isobutylene in the presence of sulphuric acid; (8) secondary butyl tertiary butyl ether from secondary butyl alcohol and isobutylene in the presence of sulphuric acid; (9) isopropyl tertiary amyl ether from isopropyl alcohol and tertiary amylene in the presence of sulphuric acid; (10) methyl tertiary hexyl ether from methyl alcohol and tertiary hexylenes (prepared by scrubbing a hexane-hexylene mixture with 65 per cent sulphuric acid, diluting the acid layer with water and boiling out the hydrocarbons) in the presence of sulphuric acid; the methyl ether from tertiary heptylene and higher tertiary olefines, the ethyl ethers from tertiary hexylene, tertiary heptylene and higher tertiary olefines, the normal and isopropyl, normal, iso- and secondary butyl ethers from tertiary amylene, tertiary hexylene, tertiary heptylene and higher tertiary olefines and the normal, iso- and secondary amyl ethers from tertiary butylene, tertiary amylene, tertiary hexylene, tertiary heptylene and higher tertiary olefines may be similarly prepared; (11) the mono- and di-ethers from ethylene glycol and tertiary butylene in the presence of sulphuric acid; (12) tertiary butyl-, methyl, ethyl or n-butyl ether of ethylene glycol, from ethylene glycol monomethyl, ethyl or n-butyl ether and tertiary butylene in the presence of sulphuric acid; (13) the monoether (probably the a -ether) from 1 : 2-propylene glycol and tertiary butylene in the presence of sulphuric acid; (14) the mono-ether (probably the a -ether) from glycerol and tertiary butylene in the presence of sulphuric acid; (15) the diether (probably the 1 : 3-ether) from glycerol and excess of tertiary butylene in the presence of sulphuric acid; (16) mono-tertiary butyl ether of diethylene glycol from diethylene glycol and tertiary butylene in the presence of sulphuric acid; (17) monotertiary amyl ether of ethylene glycol from ethylene glycol and tertiary amylene in the presence of sulphuric acid; (18) a mixture of mono- and diethers by carrying out the reaction of (17) in the presence of concentrated aqueous hydrochloric acid. A sample has been furnished under Sect. 2(5) of tertiary butyl benzyl ether obtained by reacting tertiary butylene with benzyl alcohol in the presence of sulphuric acid. Polyglycols are manufactured by the elimination of one or more molecules of water from two or more molecules of glycol, which may be the same or different according to whether a symmetrical or asymmetrical polyglycol is required, or by the reaction of an olefine oxide with a glycol. Thus diethylene glycol may be obtained by the elimination of one molecule of water from two molecules of ethylene glycol, whilst ethylene propylene glycol may be produced by the elimination of one molecule of water from one molecule of ethylene glycol and one molecule of propylene glycol, or by reacting ethylene oxide with propylene glycol. The diglycols can react with another molecule of glycol to yield triglycols. The Specification as open to inspection under Sect. 91 comprises also the manufacture of mixed ethers by reacting tertiary olefines with phenols. This subject-matter does not appear in the Specification as accepted.ALSO:Essential oils, extracting.--As extraction agents for essential oils and essences may be employed mixed ethers in which one of the radicles is a tertiary alkyl group and the other is the residue of a primary or secondary aliphatic alcohol or of an aliphatic polyhydric alcohol or an ether thereof, as such or mixed with other substances. Lubricating-oils.--The mixed ethers as above derived from aliphatic polydyhric alcohols or ethers thereof may be employed as constituents of lubricants for machinery. Lacquers.--The mixed ethers as above derived from primary or secondary aliphatic alcohols may be used, as such or mixed with other substances, as diluting agents for solutions of lacquers and varnishes, e.g. of solutions of nitrocellulose in ethyl acetate. Such of the mixed ethers derived from aliphatic polyhydric alcohols or ethers thereof as are nitrocellulose solvents of sufficiently high boiling point may be used as plasticizers for cellulose esters.