1) Take a solution of sodium-thio-sulphate (hypo) and sulphuric acid in a glass beaker.
2) Place the beaker in an open place where abundant sun light is available.
3) Watch the formation of grains of sulphur and observe changes in the beaker.
4) You will notice that sulphur precipitates as the reaction is in progress.
5) At the beginning, the grains of sulphur are smaller in size and as the reaction progresses, their size increases due to precipitation.
6) Sulphur grains appear blue in colour at the beginning and slowly their colour becomes white as their size increases.
7) The reason for this is scattering of light.
8) At the beginning, the size of grains is small and almost comparable to the wavelength of blue light.
9) Hence they appear blue in the beginning.
10) As the size of grains increases, their size becomes comparable to wavelengths of other colours,
11) As a result of this, they act as scattering centres for other colours.
12) The combination of all these colours appears as white.