Chemistry Chat

To an electrolyte gel, another reactive electrolyte solution is poured on the top of the gel to form periodic bands of precipitation. The process is known as the Liesegang phenomenon, which was discovered by a German colloid chemist, R. E. Liesegang (1869-1947) in 1896. The phenomenon is easily shown in natural artistic structures like in agate formed as a result of crystallization from hydrothermal fluids. The Liesegang bands would be formed by diffusion, but the phenomenon does not have any explanation.

M. Traube (1829-1894) is known as the inventor of Traube's stalagmometer for the determination of the surface tension of liquids. In 1864, Traube dropped crystals of potassium ferrocyanide into a solution of copper sulfate. Then, the crystals were instantly coated with precipitated membrane and grow out like real living cells, which were named as artificial cells by him. Is this an “artificial cell”? Of course not, if we think of it as a model of a living cell. The phenomenon is a reaction between potassium ferrocyanide and copper sulfate to form copper ferrocyanide as a semipermeable membrane (chemical equation: 2CuSO₄ + K₄Fe(CN)₆ → 2K₂SO₄ + Cu₂Fe(CN)₆). The membrane enables the selective movement of water molecules by osmosis from the more dilute potassium ferrocyanide solution. The attraction of water into the “cell” across the membrane gives rise to an increase in the volume of the cell.

Chemical garden is an chemical experiment performed by adding metal salts such as copper sulfate or cobalt(II) chloride to an aqueous solution of sodium silicate, known as waterglass. This results in growth of plant like forms in minutes to hours. The chemical garden was first observed by an alchemist, J. R. Glauber in 1646.