HOME＞Experiments＞For Lab＞EL002 Traube Cell
The German botanist Traube, in 1864, conducted an experiment using potassium hexacyanoferrate(II) crystals and copper(II) sulfate solution, which later became known as “Traube cell.” This experiment serves as a good example for demonstrating the properties of semipermeable membranes.
This experiment uses a copper-ion-containing solution. Be sure to check the disposal method for the waste liquid beforehand after the experiment is finished.
This experiment utilizes the semi-permeable membrane properties of hexacyanoferrate(II) copper film. Water infiltrates the inside of the membrane, causing the bag-like membrane to stretch and eventually rupture. As the liquid leaks out, a new membrane forms at the liquid interface, creating a repeating process that resembles the growth of a living organism, allowing for an intriguing phenomenon to be observed.
A similar experiment using this principle is the “chemical garden.” However, because the growth takes several days and the post-processing is cumbersome, it is not suitable for student experiments. In contrast, Traube cells grow sufficiently within 10 to 15 minutes, and post-processing is much less challenging than with a chemical garden, making it a feasible experiment within a classroom setting.
Requires
equipments
・Glass containers such as vials or test tubes
reagents
・Copper(II) sulfate solution (see “Principle” column for concentration)
・Potassium hexacyanoferrate(II) (crystal granules)
Preparation
If potassium hexacyanoferrate(II) is in powder form, it should be recrystallized and made into granules.
The concentration of copper(II) sulfate solution can affect the reaction, so when comparing experiments, it is recommended to prepare a concentrated solution and dilute it as needed.
Methods
Pour the copper(II) sulfate solution into a glass container and add the potassium hexacyanoferrate(II) granules.
Observe the growth of the artificial cell starting from the granules.
Principle
The following video shows the growth of the artificial cells in 0.5 M, 0.25 M, and 0.1 M copper(II) sulfate solutions, filmed in a time-lapse over 15 minutes. The growth rate of the artificial cells differs depending on the concentration of the copper(II) sulfate solution, making this a great experiment to discuss the relationship between concentration and osmotic pressure in a classroom setting.
By the way, when I first conducted this experiment, I accidentally used a trivalent iron salt instead of the intended divalent one. Since it looked interesting, I left it for two days, and a brown object began to extend into a rod-like shape (though I’m not sure if it was an artificial cell). Interestingly, it turned out to be quite durable．
The German botanist Pfeffer conducted experiments to measure osmotic pressure using the semipermeable membrane of hexacyanoferrate(II) copper. The results of this experiment later contributed to the discovery of Van’t Hoff’s law. Since Traube’s artificial cells are fragile in their natural state, they are generated inside a porous porcelain tube for experimentation. This time, based on the experimental method from [4], I conducted the experiment using a smaller porous porcelain tube than the one used for the Daniell cell in the literature.
Requires
equipments
・Unglazed containers for Daniel batteries
・Container that fits enough unglazed containers
・Rubber stopper large enough to fit into the mouth of an unglazed container
・glass tube
・decompressor
reagents
・2 M diluted hydrochloric acid
・0.3 M potassium hexacyanoferrate(Ⅱ) solution
・1 M copper(II) sulfate solution
・50% sugar water colored with food coloring
Methods
Place the porous porcelain container into a beaker, fill the beaker with 2 M dilute hydrochloric acid, and apply reduced pressure to clean the fine debris from the porous porcelain container. After that, replace the dilute hydrochloric acid with pure water, followed by a 0.3 M hexacyanoferrate(II) potassium solution, and apply reduced pressure again.
Fill a separate beaker with 1 M copper(II) sulfate solution and submerge the porous porcelain container. After that, remove the porous container and lightly rinse it with water. If the walls of the porous container appear dark brown, it indicates that a hexacyanoferrate(II) copper membrane has formed.
Fill the porous container with sugar water and seal it with a rubber stopper that has a glass tube passing through it. The pressure will push the sugar water up inside the glass tube. Mark the liquid level in the glass tube, then place the container into a beaker of water and wait for 10 minutes.
After 10 minutes, measure the length from the liquid level that has risen inside the glass tube to the mark you previously made.
Principle
Be careful not to apply too much force when fitting the rubber stopper, as it could cause the porous ceramic tube to break.
reference
[1] 豊田太郎，“人工細胞の化学 ” 化学と教育，70(12)，2022，578-581
[2] 二宮章夫，“顕微鏡を使用した化学実験(Ⅲ)ーフェロシアン化物の半透膜ー ” 化学と教育，40(1)，1992，50-51
[3] 白井光太郎，“植物病理學講義” 植物學雑誌第二十一號，2(21)，1888，214-219
［4］原成介，“浸透圧実験器(使ってみよう理振機器 (15))” 化学教育，33(4)，1985，318-319
・岩田久道，“死海の水から豆腐・トラウベの人工細胞ー濃度の効果的な授業展開ー” 化学と教育，55(4)，2007，172-175
・小林邦佳，“半透膜の性質に関する実験” 化学と教育，59(5)，2011，262−263