Summary
The paper presents two demonstrations of the so-called “shaken-not stirred” experiments, which show the immiscibility of five or six layers of liquids. The setup of both demonstrations is such that one homogeneous layer in a multiphasic mixture separates into two new layers upon shaking. The solvents used are methanol, toluene, petroleum ether or n-pentane, silicone oil, perfluoroheptanes, and water for the five-layer demonstration.
The first demonstration starts with methanol colored with methyl red. Addition of perfluoroheptanes results in a simple biphasic mixture. In the next step, toluene (colored with Sudan III) is added and the mixture stays biphasic. It does not matter whether stirred or shaken, it is impossible to obtain three layers. After carefully adding saturated aqueous potassium carbonate solution (colored by copper (II) ions), the solution is stirred with a glass bar and three layers remain. Now, the solution is shaken, not only stirred, and a fourth layer develops! In the next step, silicone oil is added, and the solution is stirred again. But there are still four layers. Finally, viscous petroleum ether is added, and the solution is shaken, not stirred, and left for some minutes. The former toluene–silicone oil layer separates and five layers are observed.
The second demonstration again starts from methanol colored with methyl red. Addition of perfluoroheptanes yields a mixture with two layers. n-Pentane colored with Sudan III is added, the mixture is stirred and shaken, but only two layers can be observed. A three-phase system can be obtained by careful addition of saturated aqueous potassium carbonate solution, colored by copper (II) ions. The mixture is stirred, not shaken, and three layers remain. Next, the test tube is shaken and an additional fourth layer develops as the red layer separates into two red layers. Silicone oil is added, the mixture is stirred again, and four layers remain. Finally, after the addition of petroleum ether and shaking of the mixture, five layers develop. As in the first demonstration, only a couple of minutes are necessary to perform the complete experiment. This mixture can be shaken again and again and separates again into five layers in several minutes at most.
The “shaken-not stirred” experiments combine the nonmiscibility of several solvents with the behavior of hydrocarbon–methanol–water mixtures when the water layer contains salt such as potassium carbonate. When the mixtures are stirred, the salt concentration in the aqueous phase does not disturb a homogeneous methanol–hydrocarbon layer. But when the contact surface between the layers is enlarged by vigorous shaking, the interaction of potassium carbonate with the three solvents hydrocarbon, methanol, and water forms three layers from two. Whether the whole cocktail finally contains four or five layers depends on which of the additional components, fluorocarbon and silicone oil or heavy petroleum ether, have been added.
