122 EXPERIMENT STATION RECORD. [Vol. 41 



on soil properties are reviewed. Most of these studies are said to deal with 

 soil properties other than colloidal, and with methods other than those em- 

 ployed in colloid chemistry. The results of a rather critical study of different 

 methods for measuring coUoidality and of certain difficulties encountered in 

 attempting to apply various methods are also presented and the details of the 

 methods finally developed for use in these investigations described. The 

 methods comprise a modification of Mitscherlich's water-vapor-adsorption 

 method (E. S. R., 17, p. 838), a modification of Ashley's dye-adsorption method,' 

 and the so-called suspension method. 



Observations were made on the effect of drying upon the adsorption of dyes 

 by artificial preparations of the principal colloidal materials found in the soil ; 

 the effect of different factors on hygroscopicity in the soils studied by the 

 water-vapor-adsorption method including time, remoistening, the permanency 

 of the effect of drying, alternate wetting and drying, drying at high tempera- 

 tures, long immersion in water, and leaching ; the adsorption of various dyes by 

 differently treated soils; the amount of Clyde soil subjected to different mois- 

 ture treatments remaining in suspension in distilled water and in 4 per cent 

 ammonia 30 minutes after shaking; the effect of alternate wetting and drying 

 on the amount of hunius extracted from a Clyde soil ; the relative intensities 

 of water extracts of Dimkirk and Clyde surface soils ; and the chemical nature 

 of soil colloids. The results of the experimental work may be summarized as 

 follows : 



The adsorption of water vapor was not materially affected by variations of 

 from 5 to 10° between 15 and 40° C. The chemical composition of certain 

 soil-forming minerals affected the adsorption of dyes, acid dyes as a rule 

 being more strongly adsorbed by basic minerals than were basic dyes, while the 

 latter were more strongly adsorbed by acid minerals. Diamin sky-blue, one of the 

 few dyes strongly adsorbed by colloidal ferric oxid, was adsorbed the most 

 strongly of all those examined. It was also adsorbed by alumina, but not by 

 silica. An alga and a fungus adsorbed considerable amounts of the dyes used, 

 indicating that the growth of lower forms of plant life in the soil affects its 

 adsorptive capacity. Both air-dried and oven-dried colloidal silica, alumina, 

 ferric oxid, and humus, immersed in dye solutions, showed a reversal of their 

 capacity to adsorb dyes, and also adsorbed water vapor rapidly. 



The difference in hygroscopicity between a moist and an air-dried soil was 

 found to persist for three months at least, while remoistening air-dried soils to 

 a moisture content above that originally held did not cause a reversal of 

 hygroscopicity immediately nor within three months. The alternate wetting 

 and drying of soils did not affect the hygroscopicity after the first drying. Sub- 

 soils that had been wetted and dried 32 times showed a significant cumiilative 

 decrease in hygroscopicity. Hygroscopicity decreased successively with air- 

 drying, oven-drying, and ignition, the change from the moist to the air-dry 

 condition producing a greater change than that from the air-dry to the oven- 

 dry, while the change from the oven-dry to the ignited condition was greater 

 than from the air-dry to the oven-dry condition. Some ignited soils had com- 

 paratively high hygroscopic values. Long immersion under water increased 

 the hygroscopicity of a soil poor in organic matter, and decreased it in one 

 rich in organic matter. Leaching a soil Increased its capacity for adsorbing 

 water vapor. 



Oven-drying and ignition reduced the adsorption of methylene blue. Clyde 

 soil, rich in organic matter, showed less effect due to drying than did the other 

 soils, this being contrary to the results secured with water-vapor-adsorption. 



lU. S. Geol. Survey Bui. 388 (1909) pp. 1-65. 



