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Do Polar BearsGet Lonely?
THE LAST WORD
Bad soap
I found this forgotten bar of soap
(see photo, above) after winter at
my home in northern Sardinia . It had
grown a coat of mould. What is the
mould and how did it grow on soap,
which is supposed to keep your
hands clean?
■ We use soap for cleaning because it is a detergent: a means of emulsifying insoluble, largely fatty, dirt in water. Its nutritional value is usually irrelevant, but pure traditional soap consists of fatty-acid salts. Because of this, it is completely digestible in modest quantities. You may see a dog scoffing a chunk of soap because it smells appetisingly of fatty acids, but only if it doesn’t contain too much scent or lye – sodium hydroxide, which is used in the production process. Missionaries who introduced soap to some tribal communities in Africa were startled to find that members of
their congregations would treasure a fatty-tasting bar as a treat, occasionally licking a finger that had been moistened and rubbed on the soap.
Toilet soap commonly contains surprising amounts of starches, oils, glycerol and other materials that make it smoother, less aggressive to the skin or simply cheaper to produce. These are all edible too, and moulds are happy to consume them. As long as the soap doesn’t contain too much sodium and the air is moist enough, as it well might be in a bathroom, a bar of soap can certainly grow some very contented fungi.
I suspect your soap sported a selection of Sardinian domestic moulds. Fusarium, Mucor, even white strains of cheese fungi, such as Penicillium camemberti, might be present. They are probably harmless. Try some if you like…Jon RichfieldSomerset West, South Africa
Though we admire Jon Richfield’s desire for direct scientific experimentation, we recommend that you do not eat the soap before finding out exactly what is growing on it – Ed
■ While I can’t help your reader identify the strain of mould on the soap, I can explain how mould can grow on something that is used for cleaning your hands.
Soap consists of long-chain organic molecules, with one end that is polar (charged) and the other non-polar (uncharged). The polar end readily dissolves in water, which is also polar, while the non-polar chain readily attaches to grease and oil which are similarly non-polar.
The soap therefore acts as a go-between: one end attaches to the oil and the other end wants to be in the water. This enables the oil on your skin to dissolve and be washed off. Without the soap, the polar water molecules would rather stick together than attach themselves to the oil on your hands.
Mould can grow on all sorts of apparently uninviting materials, including leather or wallpaper. Soap is no different – it’s just another organic material. This is not really a paradox. After all, when you use soap you don’t actually leave it on your hands in order for them to stay clean; you wash it off.Simon IvesonSchool of EngineeringUniversity of NewcastleNew South Wales, Australia
THIS WEEK’S QUESTIONSBEE ALERT
When I was wandering around my garden one evening I noticed a European honeybee hanging strangely from a lillipilli flower. On closer inspection I saw a well-camouflaged spider holding the bee in place and a number of small flies covering its body (see photo, below). I can understand the spider’s role in all this, but what are the flies doing? Robert McKinlayBalgownie, New South Wales, Australia
AERIAL GLUE
I heard that a Formula 1 car travelling at 200 kilometres per hour would generate enough downforce (or suction) to allow it to stick to the ceiling. Is this correct? And if it is, how is the force generated?Robert WebberMelbourne, Australia
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