Abstract

Chemistry is concerned with all aspects of the changing of one kind of matter into another. It has many parts and all but one of these are so different from all the adjacent sciences that their distinctness is obvious; the exception is physical chemistry. The activities of its practitioners resemble prima facie those of physicists. These however deal with unchanging matter that retains its chemical identity, and virtually all their experimental information is numerical. The physical chemist's concerns are the nature, extent, and rate of chemical changes, and on these much information may be gathered by the observer's unaided senses.A fundamental feature or chemistry with few parallels in other sciences is that the variables determining chemical behaviour include the purity of reaction vessels, reagents, and the gas-phase in contact with these, as well as the exact experimental procedures when bringing about the chemical changes. For this reason, when encountering ostensibly new chemical phenomena, it is even more important than in other areas to distinguish between repeatability (of phenomena, e.g. explosions) and reproducibility (of quantities, e.g. reduction potentials). The distinction is not always clear, as differences of degree may develop into differences of kind. Unrepeatability may be of great heuristic significance, but irreproducibility is often of trivial origin. Examples from the author's researches illustrate how chemical behaviour, e.g. electrochemical conductivity or the nature of a product, such as the shape of a polymer molecule, can be altered profoundly by very small changes of experimental conditions, which is uncommon in other sciences.