Dutrochet Osmometer

Quick Answer: The Dutrochet osmometer is a classic osmosis apparatus: a funnel-shaped vessel closed by a partially permeable membrane and fitted with a narrow upright tube. Filled with sugar solution and dipped in water, it shows the liquid climbing the tube as water enters by osmosis.

The Principle Behind the Dutrochet Osmometer

The apparatus is named after Henri Dutrochet, the French physiologist who studied the passage of water through animal and plant membranes in the 1820s and introduced the terms endosmosis and exosmosis. His arrangement is still the clearest way to show osmosis to a class: a concentrated sugar solution sits inside the vessel, pure water sits outside, and only a membrane separates them.

Water molecules cross the membrane in both directions, but more move from the dilute side, where the water potential is higher, into the concentrated solution. The extra volume has nowhere to go except up the narrow tube, so the level rises visibly within minutes to hours. Because the tube is narrow, even a small volume of water entering produces a large rise, which is what makes the effect easy to measure against a scale or a marker line.

Real membranes such as cellophane, dialysis tubing or parchment are partially rather than perfectly permeable. Sugar slowly leaks out as water flows in, so the rise slows, stops and may reverse over a long run. That behaviour is a useful discussion point, and it is why later instruments such as Pfeffer’s osmometer of 1877, which used a precipitated copper ferrocyanide membrane, were needed to measure osmotic pressure properly.

Specifications

Experiments with the Osmometer

• Demonstrating osmosis and water potential in secondary biology
• Timing the rise of liquid in the tube and plotting height against time
• Comparing sugar solutions of different concentration to show that a steeper gradient gives a faster initial rise
• Linking osmosis to root hair uptake, turgor and plasmolysis alongside the potometer
• Chemistry lessons on colligative properties and osmotic pressure

Setting Up and Caring for the Apparatus

• Tie or clamp the membrane tightly over the mouth of the vessel and check for drips before immersing it; a single leak ruins the reading.
• Add a little food dye to the sugar solution so the rising column is easy to see from the back of the room.
• After use, discard the membrane, rinse sugar out of the tube with warm water before it dries and turns sticky, and let the glass drain.
• Support the long tube in a clamp stand rather than letting it lean, because narrow glass tubing snaps easily.

Why Choose LabEquip

Biology and chemistry departments order this osmometer as a demonstration piece that a whole class can watch at once. LabEquip lists it with its biology lab products; send your requirements through the contact page to confirm the parts supplied.

Frequently Asked Questions

What membrane should I use in a Dutrochet osmometer?

Cellophane sheet, dialysis (Visking) tubing and parchment paper all work because they let water pass faster than sugar. Historically, animal bladder was used. The membrane must be wetted, stretched flat and tied tightly, with no creases where the solution can seep out.

Why does the liquid stop rising after a while?

Two things slow it down. The rising column creates hydrostatic pressure that pushes water back out, and some sugar leaks through the membrane, reducing the concentration difference. Once these effects balance the inward flow of water, the level stops changing.

Can salt solution be used instead of sugar?

It can, but small ions cross most classroom membranes more easily than sucrose molecules, so the rise is smaller and fades sooner. Sucrose gives a clearer, longer-lasting result for demonstrations.

How is the Dutrochet osmometer different from a potato osmoscope?

Both show water moving into a more concentrated solution. The potato osmoscope uses living plant tissue as the membrane, so results vary with the potato. The Dutrochet apparatus uses a known artificial membrane and a narrow tube, which makes the rise easier to measure and repeat.

Does the osmometer measure osmotic pressure exactly?

No. It shows the direction and relative speed of osmosis. Because the membrane leaks solute and the column height changes during the run, it gives only a rough indication. Accurate osmotic pressure or osmolality values come from dedicated laboratory osmometers.

How should students record the results?

Mark the starting level on the tube or scale, then note the height every few minutes. A table of time against height, drawn as a line graph, shows the fast early rise and the levelling off, which students can then explain in terms of water potential.

Last Updated: September 2026