The olefines may be synthetically prepared by eliminating water from the alcohols of the general formula CnH2n+1 OH, using sulphuric acid or zinc chloride generally as the dehydrating agent, although phosphorus pentoxide, syrupy phosphoric acid and anhydrous oxalic acid may frequently be substituted.
Fittig and his pupils (Annalen, 1883, 216, pp. loo, 115; 1885, 227, pp. 55, 119), in which it was shown that the aldehyde forms an addition compound with the sodium salt of the fatty acid, and that the acetic anhydride plays the part of a dehydrating agent.
Its powerful affinity for the elements of water makes it a valuable dehydrating and condensation agent.
For external use, sulphuric acid is a powerful irritant and caustic, acting by its powerful affinity for water and therefore dehydrating the tissues and causing them to turn black.
Water soluble lubricating gels can moisten the lips without the dehydrating effects of glycerol and paraffin based products.
