In 1748 Jean-Antoine Nollet made a discovery that would prove more important to modern science than all of Galileo's astronomical discoveries from the century before. He had discovered osmosis. Osmosis explains how kidneys clean our blood, how plants control photosynthesis and, in part, how cells control their internal environment. It has many more applications in biology, civil engineering and chemical engineering. History is fickle. The Abbe and his discovery have not received the attention they deserve.
Jean Antoine Nollet was a Catholic priest from the eighteenth century who was an advocate for the study and teaching of science in France. He became known as Abbe Nollet. His main area of experimentation was electricity. In 1748, Abbe Nollet conducted an experiment where he took a vial of alcohol, covered it securely with some pig's bladder then submerged it into a container of water. Abbe Nollet was careful to purge the alcohol of any air. Upon returning 6 hours later, he noticed that the piece of pig's bladder was bulging. On pricking the bladder, liquid from inside the vial shot 1 foot (30 cm) into the air. Suspicious that heat might somehow involved, he retried the same experiment accounting for temperature, and discovered that heat was not a factor. [_1_] .
This experiment was tremendously important. Human beings, like many animals and plants, are mostly composed of water. A means of moving water without an external input of energy had been discovered. There was another benefit that wasn't so obvious. Water in biological systems contain chemicals in solution. The concentration of the chemicals is very important. When the concentration of some chemicals is too low it can hinder biological processes and when too high, might be toxic. Osmosis is a low-energy means used to help regulate these concentrations.
The pressure developed from osmosis in Abbe Nollet's experiment tells us that osmosis might have mechanical applications. Photosynthesis and respiration in plants depend on the supply and release of Carbon Dioxide and Oxygen. This is controlled by gas valves known as stomata (found on the bottom of leaves). Stomata are opened and closed mechanically through the swelling or constriction of guard cells due to osmosis.
The main agent in osmosis is the semi-permeable membrane. These membranes have 'pores' that allow some molecules through and repulse other molecules. Solvent molecules (water) can pass through the membrane but solute molecules (e.g. salt or sugar) cannot. There's got to be more to it, however. The Abbe noticed a net increase in solvent on one side of the membrane. But solvent molecules can pass through the pores in a semi-permeable membrane as easily in one direction as the other. There should be no net increase on either side unless the solute (salt or sugar) is interfering with the process.
So what is happening? In the diagram above, Side B has only solvent molecules, and Side A has solvent and solute molecules. Lets also say that there are the same number of solvent molecules on either side. If the levels on Side A and Side B donot stay the same it might mean that the solute (e.g. salt) is interfering with the ability of solvent (e.g. water) on Side A to enter the pore. In fact, when solute molecules are repulsed by the membrane, their momentum away from the membrane is transferred to nearby solvent molecules, preventing them from reaching the pores. Fewer free solvent molecules are available at the pores on Side A. The availability of solvent at the pores on Side B hasn't changed. Over time this imbalance means that solvent (water) will build up on side A.
The short animation below gives you an idea of what is happening at the molecular level.
It is possible to know the what and how of a natural process without knowing the why. Abbe Nollet discovered osmosis in 1748 and in the following centuries its importance to biological systems was recognized. In spite of these advances, a proper understanding of the mechanism by which osmosis works had to wait until 1951, two centuries after Abbe Nollet's discovery. Even after the mechanism for osmosis was discovered, it did not make its way in to all medical, plant physiology, and biology textbooks. In some cases the wrong mechanism for osmosis is still being taught today.
You would expect the fame of an experiment and its author to correspond to their importance. That is not true with Abbe Nollet. It is not true with many other important experiments. Meanwhile, an experiment that never happened, Galileo's Tower of Pisa Experiment, is probably the most famous experiment in the history of science (see The Tower of Pisa Myth). Abbe Nollet was only one of many priest-scientists who made important discoveries or founded scientific disciplines (see List of Catholic Clergy Scientists). Because of the strange workings of popular history, few are recognized.