There is compelling evidence that the writers responsible for the impenetrable prose of social security forms are now moonlighting as advertising copywriters. A recent perfume ad tells us that the “notes combine to produce a scent that seems to subtly alter each time you smell it”. What can this mean?

Despite the ads there is some good science in perfumery. Perfumes have always been obtained from plant and animal sources. Animal extracts are an improbable origin for expensive high-fashion perfumes. For example, ambergris is a grey waxy solid found in the intestines of sperm whales. It was used to give permanence to some components of perfumes.

As most people know, the problem with perfume is that it often lacks staying power - and it can change on the skin. All perfumes are mixtures, sometimes containing hundreds of components. Since these evaporate at different rates, the smell of the perfume will alter with time. The three main stages are: * the main scent - this will often evaporate and disappear within an hour; * the heart scent - this may last for two or three hours; * the body of the scent - with luck this may last a day.

Perfumes applied to the skin will inevitably mix with sweat. This partly accounts for the variation in smell when the same perfume is worn by different people.

Sealed vials of perfume have been recovered from the wreck of the Titanic and the perfume has been analysed to identify its components. Its smell resembles a mixture of violets and roses. A recreated version is to be marketed as “Heart of the Ocean”. Is this more evidence for the power of words?

Trapping the perfume of a flower is a complex business. The traditional method was enfleurage. Glass panes were covered in a layer of solid fat, about 1cm thick on both sides. Fresh flower blossoms were sprinkled on the fat. Each glass sheet, held in a wooden frame, was added to a stack and left for a day. The faded blossoms were then replaced with new ones after first mixing the fat to expose a fresh surface. After three weeks, the fat contained enough flower perfume for the next stage, and was chopped up and mixed with a solvent, such as alcohol. The solvent extracted the perfume, giving a concentrated solution, such as essence of jasmine.

The remarkable thing is that mixing these flower essences reproduces the smell of other flowers. For example, essences of jasmine and orange flowers combine to give the smell of sweet peas. This process is the basis of making new perfumes by mixing natural or artificial ingredients.

Distillation can take credit for much human happiness. Perfumes, and spirits such as vodka and gin, rely on this separation process. On the internet you (but hopefully not your students) can find perfume recipes that combine both pleasures. One recipe for lemon spirit cologne starts with the following: * 1 cup of vodka * 3 drops of lemongrass essential oil * 10 drops of lavender essential oil ...

Essential oils are natural volatile oils produced by plants. They are responsible for the aromatic scents of some plants. These oils may be found in the rind of fruit, in leaves, wood, bark or even seeds. Some plants may produce several oils. The orange plant produces three varieties - one from the rind, another from the plant’s leaves and a third from the flowers. The orange-flower oil was supposedly named after the emperor Nero, and hence is known as neroli.

The steam distillation process is very simple. The fragrant part of the plant is placed in water. As the water boils, the volatile oils distil along with the steam. The oils are almost immiscible, but enough dissolves in the condensed steam to give the water a weak scent, like rose water.