Bar or cake?
I put some new soap in the cloakroom earlier. The soap already in there was looking grimy, with great dark fissures in it. When I was teaching, I always insisted that soap should be washed after use. If the dirt from hands remains on the surface of the soap, all too soon deep cracks appear.
Obviously, I haven’t been insisting strenuously enough – or even at all! - at home. It’s no good saying, ‘It’s clean dirt’ – that is, from the garden soil – the effect will be the same.
Why does soap get like that? I found this, which explains it more clearly than I can:-
Soaps are simply mixtures of sodium or potassium salts derived from fatty acids and alkali solutions during a process called saponification. Each soap molecule is made of a long, non-polar, hydrophobic (repelled by water) hydrocarbon chain (the "tail") capped by a polar, hydrophilic (water-soluble) "salt" head.
Because soap molecules have both polar and non-polar properties, they're great emulsifiers, which means they can disperse one liquid into another. When you wash your dirty hands with soap and water, the tails of the soap molecules are repelled by water and attracted to oils, which attract dirt.
The tails cluster together and form structures called micelles, trapping the dirt and oils. The micelles are negatively charged and soluble in water, so they repel each other and remain dispersed in water—and can easily be washed away.
Not only should soap be rinsed after use, it should be patted dry with a cloth. Otherwise, it should be left to air-dry, which is what I and I guess most people do, or have I been living in ignorance all my life? Another suggestion is not to leave it in a wet or humid area, so make sure your bathroom is well-ventilated, preferably with a stiff breeze blowing through it. 😉
As I removed the disgusting-looking but pleasantly scented soap to be used where it would not give visual offence, and replaced it with fresh-smelling clean lavender soap, I pondered why some people speak of bars while others insist on cakes of soap. Was there a difference and did it matter?
The short answer was that the only difference lies in the shape of the soap. A bar of soap is rectangular or oval while a cake of soap is moulded into shapes that look like little cakes, but can also be rectangular or oval. Some are formed into little hearts or shells or animals.
I think, also, that cakes of soap are usually smaller than bars of soap. So-called ‘guest soaps’ are usually unfeasibly small and are of little use for more than a delicate dip in the water.
Another source informed that a cake of soap is an old-fashioned name for a bar of soap. It may have arisen because soap was manufactured in large bars. The required length was then cut off, just as a cake is sliced. In the same way, we have ‘bars of chocolate’ and ‘gold bars’.
