made a specialty of generalizations applicable to all branches of chemistry.
As Bancroft saw it, physical chemistry's central role in chemistry and chemistry's central position among the sciences gave practitioners of his young specialty special opportunities and responsibilities. Many of the problems and phenomena of geology, biology, and industry were known to be related, although the structure of science and scientific institutions often seemed to obscure those relations. Physical chemists, by defining themselves as students of change rather than as masters of some particular form of matter, could appreciate similitudes and affinities lost upon those with narrower training and ambitions. Their knowledge gave them license to act as intellectual brokers—middlemen who might prosper by matching techniques to problems, regardless of traditional patterns of interaction among the sciences. In Bancroft's view, wherever matter underwent alteration, whether in the interior of the earth or in stars, in human bodies or in industrial vessels, the physical chemist could both learn and teach.13
Before physical chemists could meet their duties as generalists, Bancroft believed they would have to find a rational system for organizing their subject. Entering the field at a time when it was expanding rapidly, Bancroft felt need of a structure into which might be fit that which was known and that which was yet to be learned. "There has been so much work done in physical chemistry during the last ten years," wrote Bancroft in 1897, "that the mass of accumulated material is now too large to be remembered as miscellaneous facts. It becomes comparatively easy to survey the whole field if we consider the phenomena as examples illustrating a few general principles."14
The classificatory scheme on which Bancroft settled first divided physical chemistry according to whether the ideas