I have been occupied with the following ideas and experiments for several years. Therefore the subject is of such great interest to me that I may not see with a clear eye all the deficiencies of the method described here, and I may overestimate its value.
Langmuir, one of the most famous physicists, found that some substances can be spread on a watery surface in a layer that is only one molecule thick. Palmitic acid, for example, may be dissolved in petroleum ether, and a small, accurately measured amount of the solution placed on the surface of water in a large tray. After evaporation of the solvent a barrier can be moved in such a way that the surface is gradually diminished in size and the molecules of the fatty acid are brought together. When the molecules have all come into contact with each other the surface tension suddenly diminishes.
GORTER E. SPREADING IN A MONOMOLECULAR FILM: A METHOD FOR STUDYING BIOLOGIC PROBLEMS. Am J Dis Child. 1934;47(5):945–957. doi:10.1001/archpedi.1934.01960120003001
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