Nobel Lecture by Jacobus H. van’t Hoff

Endosmometer by Dutrochet

I am amazed by the excellent work of notable scientists who developed and used “crude” instruments to bring us to where we are today and for expectations for further advances in all sciences. 

Endosmometer by Dutrochet
Endosmometer by Dutrochet

Review and Discussion  

Osmotic Pressure and Chemical Equilibrium   by Jacobus H. van’t Hoff   Nobel Lecture, Dec 13, 1901

Van’ Hoff’s theory was the first Nobel Prize in Chemistry…  He showed that Osmotic pressure is proportional to solute concentration for dilute solutions.   This model based on the newly developing model for a perfect gas introduced thermodynamics to the osmosis experiment.

Osmotic pressure is applied to the solution side of the membrane to stop the flow of the solvent ‘water’ from flowing through the membrane into the solution.      Osmosis comes from the Greek word for push.    Many others had conducted the experiment and looked at the data.  But van’t Hoff was the first to relate osmotic pressure for dilute solutions to the model for a perfect gas.    Osmotic pressure is an important variable in chemistry, botany, biology, and other fields. 

Experimental results showed osmotic pressure was related to plant and animal cells, and to geological substances which bonded with water.    Cell water content varies with the osmotic pressure of the solution it is placed into.  So, it was assumed that Osmotic pressure must be acting with in the cell. The product from Reversible chemical reactions can also be controlled with pressure.   And dynamite explodes completely when unconstrained.  In a pressure vessel, a portion of the dynamite remains unexploded.   In conclusion, the “laws of osmosis have proved to be very fruitful in the field of chemistry …osmotic pressure plays a fundamental role in plant and animal life…”     


After van’t Hoff’s work became public, others noted that osmotic flow model indicated flow from a low pressure through the membrane to a higher-pressure region.   Osmotic pressure was such a useful variable, that discrepancies were explained in terms of fugacity, virial coefficients, etc.   Each field developed its own means to explain osmotic flow.     The missing link was a fundamental application of basic physical laws to the osmosis experiment.  These fundamentals are:  Mass balance, Force Balance (Newtons laws of motion), and Energy Balance.  The osmosis experiment must be analyzed as a three-stage process.  (1). Pure water, (2). Introduction of solute to one side of the membrane, and (3). Applied osmotic pressure to stop flow of water through the membrane.  Mass, force, and energy balance must occur for each stage of the osmosis experiment.  That is why an engineering approach was essential for a more complete understanding of the osmosis and osmotic pressure.

©   Larry Howlett     HTMD Engineering     2020

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