Baking soda is common name for Sodium bicarbonate or NaHCO3. Sodium bicarbonate is a white solid that is crystalline but often appears as a fine powder which has several household and industrial uses. Crystals are solid materials made up of atoms, molecules or ions arranged in a repeated or ordered pattern forming three-dimensional structures. Baking soda can transform into its crystalline structure when it is in high concentration. When the solution of baking soda is saturated, the crystals will form in the walls of the container. If you place a string above the solution, the crystals will start to grow there. Saturated solution simply means that a liquid (or solvent) is holding as much of solid it can hold OR it has dissolved the entire solid it can hold.