HYSTERESIS I N SORPTION.
VI
531
REFEREKCES
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (21) (22) (23) (24)
ALLMAND,HAND,A N D M A N R I N GJ.: Phys. Chem. 33, 1694 (1929). ANDERSOK: 2. physik. Chem. 88,212 (1914). COHAN:J. Am. Chem. SOC.60, 433 (1938). FREGNDLICH A N D ROSEXTHAL: Kolloid-2. 37, 129 (1925). LAMBERT A X D CLARK:Proc. Roy. SOC.(London) Al22, 497 (1929). LAMBERT AND FOSTER: Proc. Roy. SOC.(London) A136,363 (1932). MCBAIN:J. Am. Chem. SOC.67, 699 (1935). MCBAIN:T h e Sorption of Gases and Vapours by Solids, p. 433. George Routledge and Sons, Ltd., London (1932). MCBAIN:Reference 8, page 443. RIDEAL:Trans. Faraday SOC.32, 4 (1936). RIDEAL:A n Introduction to Svriace Chemistry, p. 444. University Press, Cambridge (1930). RAO,K. S.: J . Phys. Chem. 46, 500 (1941); Paper I. RAO,K . S.: J. Phys. Chem. 46, 506 (1941); Paper 11. RAO,K. S.: J. Phys. Chem. 46, 513 (1941); Paper 111. RAO,K . S.: J. Phys. Chem. 46,517 (1941); Paper IV. RAO,K. S.: Current Sci. 8, 256 (1939). RAO,K. S.: Current Sci. 8, 516 (1939). RAO,K. S.: Current Sci. 9, 19 (1940). RAO,K . S.: Current Sci. 9, 68 (1940). RAO,K. S.: Current Sci. 9, 70 (1940). RAO,K. S., A N D RAO,B. S.: Proc. Indian Acad. Sci. A4,562 (1936). TAYLOR: A Treatzse o n PhyszcaZ Chemistry, Vol. 11, p. 1661. Macmillan and Co., Ltd., London (1931). THOMSON: Phil. Mag. [4] 42,448 (1871). WEISER: T h e CoZZoidaZ Salts, Vol. 111, p. 374. John Wiley and Sons, Inc., New York (1933).
HYSTERESIS IN SORPTION. VI DISAPPEARANCE OF THE HYSTERESIS LOOP. THE R ~ L E OF ELASTICITY OF ORGANOGELS IN HYSTERESIS IN SORPTION.SORPTION OF WATERON SOMECEREALS K I T T U R SUBBA RAO
Department of Chemistry, Central College, University of Mysore, Bangalore, I n d i a Received M a y 9, 1940
After the observation made of the unique and interesting colloidal behavior (3) of rice grains, in that they lost, after a series of sorptions and desorptions of water vapor, the hysteresis loop initially exhibited by them, a few other members of the plant species were studied. Gum arabic (4) has shown similar behavior in the sorption of water. A study of the sorption of water on activated dhal grains (Cajanus indicus) and of
532
KITTUR SUBBA RAO
carbon tetrachloride on a sample of the activated rice grains, presented in this paper, has thrown further light on the view that has already been put forth about the rble in hysteresis in sorption of the elasticity (3, 4) of organogels which swell on the imbibition of water. Few experiments on hysteresis in sorption on organic natural colloids are on record. The intensive and pioneer work of Urquhart (8) and his collaborators has shown the hysteresis effect in the sorption of water vapor on cellulose. I n a study of the sorption of water vapor on cellulose and its derivatives, Sheppard and Newsome (7) have observed the hysteresis loop becoming smaller in three successive cycles of sorptions and desorptions. They state, “We do not feel that a complete explanation of the hysteresis phenomenon is yet available.” B. S. Rao (2) and co-
FIG. 1. Sorption of water on activated rice grains. A, first sorption ( 0 ) and desorption ( 0 ) ;B, second sorption ( 0 ) and desorption ( 0 ) ;C, third sorption ( 0 ) and desorption ( 0 ) .
workers have expressed the view that rice is essentially a colloid having the characteristics of a gel. This view can be extended to all other grains and plant materials. EXPERIMENTAL
The spring technique, described in Paper I, was employed in the present work. I n all the experiments, the activated cereals were degassed in a vacuum (10-2 mm.) at 3OoC. for 5 hr., before a series of sorptions and desorptions of water vapor at 30°C. was conducted. To ensure complete attainment of equilibrium, about 24 hr. were ordinarily allowed. SORPTION OF WATER ON THE ACTIVATED RICE GRAINS
Experiment No. 1 The results of the first experiment presented in the preliminary communication (3) are referred to here, and all the experimental details are
HYSTERESIS I N SORPTION.
533
VI
given. The isotherms are reproduced in figure 1, in order to facilitate comparison. The rice grain (Nagapur Sanna) used in all of these investigations was aged about two years from the harvest of the paddy. The paddy was husked, and the grains were polished in order to remove the bran layer. The rice grains were activated by heating to 65%. in a vacuum for 6 hr. On activation the rice grains lost 12.5 per cent of water. A period of two months elapsed between the commencement of the first sorption and the completion of the third desorption. At the end of each sorption, the rice grains were kept in contact with water vapor at saturation pressure for 1 day. The sorptive capacity of rice a t saturation pressure in the three cycles was found to be 18.8 g., 19.7 g., and 22.3 g. per 100 g. of the activated rice.
