This compound is employed technically in the preparation of the hypnotics sulphonal, trional, and tetronal.

To obtain it on a small scale a solution (sp. gr. 13) of potassium hydroxide in water is saturated with hydrogen sulphide. The resulting solution of potassium hydrosulphide is then mixed with solution of calcium ethyl sulphate (sp. gr. 1.3) and the mixture distilled from a water-bath. The crude product is dried over calcium chloride and purified by distillation (Liebig).4

Klason indicates the following as a convenient procedure.5 One litre of alcohol is poured gradually into a mixture of 500 c.c. of concentrated sulphuric acid with the same volume (500 c.c.) of fuming sulphuric acid. After cooling down, the liquid is carefully run into a solution of sodium carbonate containing 4 kilos. of the crystallised salt, ice being freely added during the operation. The mixture is then evaporated, and the greater part of the sodium sulphate which crystallises out is removed, care being taken that the reaction is alkaline during the evaporation. To the residual liquid is added a solution of potassium hydrosulphide, prepared from 800 grams of the hydroxide by passing hydrogen sulphide into its aqueous solution as before described. The mixture is then distilled from a water-bath to separate the mercaptan, About 400 grams of the crude product are obtained: it contains some ethyl sulphide, (C2H5)2S.

1 Lilienfeld, Aust. P. 63526; J. Ghent. Soc. (Abst.), 1914, 106, [i|, 919.

2 B.P. 117824, 1917. 3 B p 119250.

4 Hoscoe and Schorlemmer, "Treatise on Chemistry," 3. [i], 378.

5 Ber., 1887,20, 3411.

To remove the latter, the crude product is either distilled, or else treated with solution of caustic alkali, which dissolves the mercaptan, but leaves the ethyl sulphide insoluble. This is separated, and the mercaptan liberated from its alkaline solution by acidifying with dilute sulphuric or hydrochloric acid.

Ethyl mercaptan is a colourless, mobile liquid, with a penetrating garlic-like odour. It boils at 362°, and has the sp. gr. 0835 at 21°. It is only slightly soluble in water, but easily so in alcohol and in ether.