Archive of posts by Peter Stotereau
Why is ice clear and snow white?
Thursday, September 2nd, 2010
Snow comprises huge numbers of ice crystals with lots of trapped air between them. If we could look at a single tiny ice crystal within the snow, it would look clear.
Visible light from the sun is made up of components of different wavelength (the electromagnetic spectrum as in a rainbow; red, orange, yellow, green, blue, indigo, violet). When the light hits a single ice crystal, some of it is absorbed and some reflected back; on passing through the crystal the light changes direction due to a process called refraction, as in a prism, and can be internally reflected within the crystal.
Posted in Your Questions | 1 Comment »
Why does paint dry on the wall but does not harden when in the tin?
Wednesday, July 21st, 2010
There are two basic mechanisms by which paints dry on the wall.
Many modern paints are largely water-based. As we know, water readily evaporates. However, the rate of evaporation of a liquid depends on the vapour pressure of that liquid above the surface. In a sealed tin of paint, a set vapour pressure is quickly established in the small headspace in the tin and the water in the paint does not evaporate and remains in the paint. But, when painted on the wall, the water can readily evaporate to leave a dried film of solid paint components behind – there is no build-up of water vapour pressure in a confined space as there is in the tin.
Posted in Your Questions | 4 Comments »
Can salt lose its saltiness?
Saturday, July 10th, 2010
Common salt comprises a very stable, simple chemical compound called sodium chloride, which has a salty flavour. As table salt, it typically also contains minor amounts of additives to keep it free-flowing.
As it is so chemically stable, sodium chloride will not lose its saltiness, even after being stored dry for many years. However, there are ways in which salt may appear to lose its saltiness.
Posted in Your Questions | 2 Comments »
