The police can ask a motorist to exhale through a tube containing some orange crystals. If the crystals turn blue, it shows that the breath contains a considerable amount of ethanol vapor. Soaps are produced by the reaction of metallic hydroxides with animal fats and vegetable oils. The major components of these fats and oils are triglycerides. Triglycerides are esters of the trihydroxy alcohol called glycerol and various long-chain fatty acids.
Tristearin is a typical triglyceride.
Upon reaction with sodium hydroxide, the ester bonds of tristearin are broken. The products of the reaction are the soap, sodium stearate, and glycerol. Soap is made commercially by heating beef tallow in large kettles with an excess of sodium hydroxide. Glycerol is an important by-product of the reaction. It is recovered by evaporating the water layer.