An investigation has been made of some characteristics of hysteresis in the pbysical adsorption of nitrogen on bone char, activated carbon, silica gel, and coconut-shell charcoal at 77.4 0 K. It was found that hysteresis became less pronounced in the order given, occurring only slightly in coconut-shell charcoal and only from high relative pressures in the pressure range in which the Langmuir equation was not obeyed. It was shown that it was highly probable that a true steady state was attained in the pressure determinations and that the time dependency of adsorptioll and desorption are compatible with the requirements of diffusion processes. In this paper the theories of hysteresis are reviewed 011 the basis of capillary condensation, and an alternative interpretation is suggested in terms of the theory of multimolecular adsorption.

The adsorption of nitrogen was determined at liquid nitrogen and liguid oxygen temperatures by measuring the pressure decrease of a known volume of the gas exposed to each of 20 different samples of bone blacks, activated carbons, vegetable carbons, and coconut cha.rcoals. Typical adsorption isotherms of these data are illustrated. Specific surfaces were estimated with fair accuracy from an an~lysiB of the data with the aid of the multimolecular theory of adsorption. The surfaces of new bone chars, service bone chars, and spent bone chars are compared; the ratio of the specific surface of a new char to that of a spent char may beas great as 7. The distribution of pore sizes in the adsorbents is discussed and the data are divided into five groups, each characterized by a value of n, which is defined as the maximum number of adsorbed layers possible on the surface of the material. All the samples in each group have a common isotherm when reduced to unit surface. The differential heats of adsorption are also determined from the dllta.

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Silk contains a number of acidic and basic groups. The state of combination and the behavior of these groups are important in influencing the tensile and elastic properties of the fibroin and the adsorption of moisture and dyes.As part of a broad research program of the Textile Foundation Research Associateship at the National Bureau of Standards on the acidic and basic properties of fibers, this investigation was undertaken to determine the relationship between the quantities of hydroclaloric acid and potassium hydroxide taken up by fibroin from solutions and the concentrations of those solutions. The effect of added potassium chloride was also studied. In general, it has been possible to correlate the several parts of the titration curves of proteins with their amino acid contents, but our knowledge of the rôle of the phenolic hydroxyl groups of tyrosine has always been uncertain. Silk fibroin, however, contains such a large proportion of tyrosine as to assure practically an indication of the rôle of the phenolic hydroxyl groups of tyrosine simply by the magnitude of the base-binding capacity. In order to investigate more carefully the part taken by these groups, a titration curve was obtained for methylated fibroin in which most of the hydroxyl groups had been converted into nonreactive methoxyl groups.The component parts of the titration curve of silk fibroin have been interpreted in terms of the composition of this protein.Thus the hydroxyl groups of tyrosine appear to bind base as shown by the fact that the base-combining capacity is much greater than can be accounted for by the other groups which are able to bind base.The presence of free carboxyl groups in silk fibroin is suggested by the shape of the titration curve. From the maximum amount of acid bound an estimate of the total content of free amino groups may be obtained. The effect of added salt is similar to that obtained with other insoluble proteins, namely to increase the quantity of acid or base bound at a given pH, in a manner which suggests that the combination of hydrogen ions is affected by the concentration of anions as well as by the concentration of hydrogen ions and that combination with hydroxyl ions is affected by the concentration of cations.

The carbon and hydrogen contents of samples of bone chars, charcoals, and vegetable carbons are determined by combustion in oxygen, the resultant carbon dioxide and water being weighed. The procedure for the handling of such highly adsorptive substances is set forth with a description of the necessary apparatus.A simple procedure is adopted to bring each sample for analysis to a constant weight . This consists in exposure of the sample to air saturated with water in an exsiccator for 18 hours, and subsequent heating in a helium atmosphere at 105 0 C for 18 hours. In the determination of the carbon, corrections are made for the carbonate remaining in the ash from t he combustion and for the carbonate a nd the adsorbed carbon dioxide contained in the original sample. The results are tabulated to give these separate contributions to the total carbon. A comparison is made with results for the same materials obtained by the determination of the loss upon ignition of the acid-washed residue of each sample.