W. O. BAKER 



ing another of the most fundamental concepts of the physical 

 and life sciences. This is molecular weight. In the past half 

 century, accurate methods for determination of molecular 

 weight over a wide range of levels were based largely on such 

 schemes as vapor density, and colligative property of solutions. 

 Very large particles could not be handled by these techniques, 

 even though they were the systems of greatest importance in 

 understanding natural processes and characterizing the sub- 

 stance of life. Sedimentation schemes such as in the ultracentri- 

 fuge were shown to be appropriate for these large molecule 

 systems, but there were and are many unknown properties 

 which complicate the interpretation of sedimentation theory. 

 Despite the erupting interest in this century in the mole- 

 cules of proteins, of carbohydrates, of cellular constituents, 

 and of synthetic polymers (plastics, fibers, rubbers) and the 

 great importance of measuring their size, there was essentially 

 no new method proposed until 1943. In that year, Professor 

 Peter Debye became interested in a problem of synthetic poly- 

 mer molecular weight and remembered that his old friend, 

 Professor Albert Einstein, had in 19 10 published a paper on 

 light scattering by liquids. In the most imaginative and theo- 

 retical terms, Professor Einstein had shown how the thermal 

 fluctuations in the density and, hence, refraction of a liquid 

 could be in equilibrium through osmotic tendencies. These 

 would either average out the properties of a pure liquid through 

 its volume or, in the case of a solution, would tend to homog- 

 enize the concentration. Now this theoretical beginning of 

 Einstein's was continued by Debye so that he has provided a 

 new scientific agency for the study of high molecular weights. 

 Much of the important new work on proteins, nucleic acid 

 complexes and synthetic polymers is immensely aided by this 

 theory and facility. 



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