Esters of the mineral acids are also known and may be prepared by the ordinary methods as given above. The neutral esters are as a rule insoluble in water and distil unchanged; on the other hand, the acid esters are generally soluble in water, are non-volatile, and form salts with bases. _Ethyl hydrogen sulphate_ (sulphovinic acid), C2H5.HSO4, is obtained by the action of concentrated sulphuric acid on alcohol. The ester is separated from the solution by means of its barium salt, and the salt decomposed by the addition of the calculated amount of sulphuric acid. It is a colourless oily liquid of strongly acid reaction; its aqueous solution decomposes on standing and on heating it forms diethyl sulphate and sulphuric acid. _Dimethyl sulphate_, (CH3)2SO4, is a colourless liquid which boils at 187 deg.-188 deg. C., with partial decomposition. It is used as a methylating agent (F. Ullmann). Great care should be taken in using dimethyl and diethyl sulphates, as the respiratory organs are affected by the vapours, leading to severe attacks of pneumonia. _Ethyl nitrate_, C2H5.ONO2, is a colourless liquid which boils at 86.3 deg. C. It is prepared by the action of nitric acid on ethyl alcohol (some urea being added to the nitric acid, in order to destroy any nitrous acid that might be produced in secondary reactions and which, if not removed, would cause explosive decomposition of the ethyl nitrate). It burns with a white flame and is soluble in water. When heated with ammonia it yields ethylamine nitrate, and when reduced with tin and hydrochloric acid it forms hydroxylamine (q.v.) (W.C. Lossen). _Ethyl nitrite_, C2H5.ONO, is a liquid which boils at 18 deg. C.; the crude product obtained by distilling a mixture of alcohol, sulphuric and nitric acids and copper turnings is used in medicine under the name of "sweet spirits of nitre." _Amyl nitrite_, C5H11.ONO, boils at 96 deg. C. and is used in the preparation of the anhydrous diazonium salts (E. Knoevenagel, _Ber._, 1890, 23, p. 2094). It is also used in medicine.