one. The particles were visible under the ultramicroscope and were separable from the solvent by mechanical means such as dialysis or ultrafiltration. By definition, Bancroft insisted, such heterogeneous mixtures did not obey the laws of true solution.32

By no means did all students of colloids share Bancroft's isolationism. In Zürich, the organic chemist Hermann Staudinger argued forcefully for a unionist position; many colloidal particles, he insisted, were nothing more than giant molecules which could be synthesized by classical methods from simpler units. In Paris, the dean of French physical chemists, Jean Perrin, believed that he had proved that dilute colloidal solutions obeyed the laws of solution, as did The Svedberg in Uppsala. And no less a physicist than Albert Einstein had reached the same conclusion by theoretical reasoning.33

Closer to home, Albert P. Mathews, former head of the Physiology Department at the University of Chicago and professor of biochemistry at the Medical College of Cincinnati, roundly condemned Bancroft for confusing descriptive and explanatory terms. "Adsorption," Mathews wrote, "is a name descriptive of a physical (or chemical) phenomenon. It says . . . nothing as to the cause or causes which produce the phenomenon described by it."34 Bancroft, by treating practically all processes in which colloids participated as adsorptions and their products as adsorption complexes, simply confessed his own ignorance and confused his readers:

The exact mechanism of this surface condensation or adsorption is not yet clear. The fact that the energy relations are satisfied gives us no picture at all of the mechanism of the process, and before we really understand it we must have such a picture.35

In fact, Mathews asserted, such a picture was beginning to emerge in the form of evidence that suggested that pro-



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