A way to separate the coloured compounds in a mixture. Ink is not a pure substance. It is a mixture of some coloured components (solid) in water (liquid). The activity is aimed to demonstrate the process to separate the components of ink. When we heat the ink on a watch glass, water present in is evaporated and a solid residue is left which is actually the coloured component due to which ink has some colour. The purpose of taking ink on watch glass is because we do not want to heat ink directly. If it is heated directly then we will not be able to get the solid residue.Solid will also decompose if ink is heated directly so the purpose of separation will not be fulfilled. Thus ink is taken in a watch glass which is kept over a beaker containing water. Beaker is heated so that ink is indirectly heated.