494 A. B. Beaumont 
absorption. The subsoil was known to contain large quantities of soluble 
salts, among which. were calcium magnesium and chlorine ions. As a 
consequence of this irregularity, this subsoil was eliminated from the tests 
of water-vapor adsorption. 
Effect of kind and source of dye on adsorption.— In searching for a dye 
that would be adsorbed by colloidal ferric oxide, dyes from twenty-three 
sources were examined. ‘The tests were made in both distilled water and 
approximately 0.1-per-cent ammonia water. Some of the dyes used are 
tabulated by various writers as acid dyes, and theoretically, therefore, 
would be adsorbed strongly by colloidal ferric oxide, which is basic. Only 
one, however, of all those examined was found to be adsorbed sufficiently 
strongly by colloidal ferric oxide to warrant its use. This was diamine 
sky-blue. 
The effect of the small amount of ammonia on adsorption was very 
noticeable in some instances. In some cases it increased adsorption; in 
other cases it decreased adsorption; and in still others it changed the 
intensity or color of the dye. The effect of electrolytes on the adsorption 
of dyes was pointed out by Bancroft (1914), and should not be ignored 
in working with soils. 
Effect of the chemical composition of minerals on dye adsorption. During 
the experimentation on the adsorption of dyes by artificially prepared 
colloids, it was found that the chemical composition of the material had 
a great deal to do with the adsorption. For instance, methylene blue, 
a basic dye, is adsorbed strongly by colloidal silica but not at all by col- 
loidal ferric oxide; whereas diamine sky-blue, an acid dye, acts in just 
the opposite way with respect to these two materials. In other words, 
according to this fact, neither dye is sufficient for measuring the total 
colloidal content of the soil, provided that Sup PrOxinat Ny pure colloidal 
silica and ferric oxide are present. 
In this connection it was thought advisable to ascertain whether the 
chemical composition of certain soil-forming minerals is an important 
factor in their adsorption of dyes. The minerals listed in table 3 were 
finely ground, and 1-gram samples were shaken with equal quantities of 
dyes. As far as it was possible to make them, the checks of the two dyes 
were of the same intensity. 
