ESTERS (an arbitrary modification of ether). Compound ethers, or ethereal salts, are compounds in which one or more alcohol or basic radicals are united to one or more acid radicals. They are analogous to the salts of the metals. Thus CH,COO.H is acetic acid and if the typical hydrogen of this acid is replaced by the monad radical ethyl, the resulting compound, CH.COO.C21-15, is known as ethylacetic ester. Chemically, this sub stance is analogous to potassium acetate, CH,COO.K, obtained by replacing the hydrogen of the acetic acid by potassium. The word ester was originally applied by Gmelin to compounds of the alcoholic radicals with oxy genated acids; but it has now been extended so as to include all the salts of the alcoholic radi cals. Ethyl bromide, CaIs.Br, for example, is now included among the esters. Some of the esters are prepared by the direct action of the acid upon the alcohol. In other cases a mix ture of the acid and the alcohol is distilled with the addition of sulphuric acid, zinc, chloride or other dehydrating agent. The esters may also
be prepared by treating the iodide of the alcohol radical with the silver salt of the acid, the iodine and silver combining to form iodide of silver, while the liberated alcoholic and acid radicals combine to produce the desired ester. The esters of the organic acids occur in fruits and flowers and arc also prepared artificially for flavoring purposes and for improving the bouquet of wines. The fats and oils which contain glycerine in combination with oleic, margaric and other acids may be regarded as esters, since glycerine is a triatomic alcohol. Much attention has been paid to the esters in connection with theoretical chemistry, since they are well adapted for the study of the laws of mass-action. See EQUILIBRIUM, CHEMIC.AL ; ETHER.