Nitrogen dioxide was absorbed from a mixture in nitrogen using caustic solutions varying from 2.7 t o 34.1 per cent sodium hydroxide, and acid solutions varying from 5.7 to 69.8 per cent nitric acid. Similar tests were carried out in a wetted-wall tower and in a batch absorption vessel. The observed absorption rates for NO2 were compared with corresponding rates of evaporation of water in the same apparatus under similar conditions.The rate of absorption was found to go through a maximum for pure water, and to be much less in strong acid or strong HE absorption of nitrogen oxides to form nitric acid, nitrates, and nitrites has long been a subject of much scientific and industrial interest. The chemistry of the important oxides, their reactions with one another, with oxygen, and with various aqueous solutions have been subjects of extensive investigations reported in the chemical literature, but the possible importance of diffusional resistances in the absorption process has received relatively little attention. The present paper presents the results of a study of the significance of diffusional resistances in the absorption of nitrogen dioxide by water and by aqueous solutions of nitric acid and of alkali.Of the various oxides of nitrogen, only NO, NzOa, NOZ, and NzOl appear to be involved in the absorption process. Nitric oxide (NO) is stable and relativeIy inactive, although it reacts with oxygen to form the dioxide (NOz) and with NOZ to form the trioxide (NzO3). These latter are absorbed by water and by caustic solutions. NOz polymerizes rapidly to an equilibrium mixture of NO2 and the tetroxide (NzOJ, and this equilibrium mixture will be referred to as nitrogen dioxide. This equilibrium was the subject of careful study by Bodenstein (S), Verhoek and Daniels (as), and others (16,19, 90, 94), and the equilibrium constant is known as a function of temperature over the range from 0' to 90' C.The reaction of NO and NOz is believed to be very rapid, although the data show that even a t moderate temperatures very little Nz03 exists in the equilibrium mixture.The reaction of NO with oxygen to form nitrogen dioxide has been the subject of much study, partly because of its industrial importance and partly because of its scientific interest as a trimolecular reaction with a negative temperature coefficient. The reaction is relatively slow, as shown by the rate constants determined in the classical studies of Bodenstein (9). These data, amplified by the results of other T 1 Present address, Esstern Laboratory, E. I. du Pont de Nemours & Company, Gibbstown, N. J.caustic. Even in the strong solutions the rate of absorption was found to be proportional to approximately the 6.8 pgwer of the gas velocity, indicating the gas-film diffusional resistance t o be controlling. The results are explained by the hypothesis of reaction in the gas phase, with the deposition of a nitric acid mist in the gas film.New data are presented on vaporization of water, desorption of ammonia from aqueous solution, absorption of ammonia by water an...

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