The complex formation between water and pyridine molecules has been studied by many researchers. A. N. Sidrov, H. Takahashi, K. Mamola and E. K. Plyler suggested the complex formation between these molecules from infra-red absorption data and J. Rouvier and J. Salvinien also suggested from the Ramann spectrum data. They found that when the amount of pyridine is much smaller than that of water, the dominant species is supposed to be pyridine-H_2O and they estimated the formation constant for the above mentioned complex as 2.8l/mol. Recently, Y. Kasugai, Y. Arata and S. Fujiwara of Tokyo University reported the presence of the above complex by using the method of NMR studies of protons and nitrogen-14 atoms. They pointed out the presence of anormalous concentration dependence of the viscosity and density in waterpyridine system. However, so long as our results are concerned, the concentration dependence of the various physical properties such as refractive index, dispersion, density and viscosity showed different curves from their results of investigations.
The NMR data they obtained showed a remarkable dependence on the concentration and especialily for the line width of the α-protons and N-14 atoms of pyridine molecules. From these results and also the facts that the N-14 spectrum of pyridine showed a single line in the whole range of concentration examined, they concluded that the complex formed in water-pyridine mixture may be considered as identical with what was given by J. Rouvier and J. Salvinien. The formation constant calculated by Y. Kasugai and their co-workers from the assumption of the relation between the line width and the fractional population of the hydrogen bonded pyridine molecules was almost identical to that of J. Rouvier and their coworkers.
In this paper, based on the theories on the refractive index and its dispersion in ideal mixture which were already derived by one of the writers, and in comparing the data of density and viscosity, the complex formation was discussed stoichiometricalily for water-pyridine and pyridine-dioxane mixtures.