564 
AGRONOMY: L. T. SHARP 
salt effects on soils, we must look to the laws formulated from studies 
on colloidal materials. Foremost among these may be mentioned those 
concerning the migration and electrical charges of colloids by Picton 
and Linde^ and the subsequent contribution by Hardy ,2 setting forth 
the important rule that ions which carry charges opposite to those 
associated with particular colloids will act as precipitants for those 
colloids. This rule could be anticipated from the previous discovery 
of Schulze^ that the flocculating power of an ion is in some measure 
dependent upon its valence. More recently Tolman^ has gone over the 
field anew, and, by assuming that stable colloidal solutions exist only 
when the surface tension between the particles and the liquid is equal 
to zero, has developed a very interesting and highly plausible theo- 
retical explanation for the phenomena occurring in dispersoid systems. 
By means of these facts we are able to predict with some assurance 
the effect accompanying the constant presence of a particular salt on 
the physical condition of a soil. It is of particular significance in this 
connection to remember, however, that these conceptions regarding the 
behavior of colloids are based on systems wherein the salt remains in 
contact with the particles. Such is rarely the case in normal field soils; 
for various agencies are constantly affecting the position of the salts, 
and as we shall see the leaching out of certain salts from a soil seems 
to produce an entirely new system, to which the laws referred to may 
not be strictly applicable. At least the conditions are suiB&ciently 
puzzHng to merit the following discussion. 
If a soil to which sodiiun chloride or sulphate has been added is 
subjected to leaching processes, it assumes an entirely new set of physi- 
cal properties, characterized by a more or less complete deflocculation.^ 
Evidently a new system, differing from that composed of the soil in 
contact with its own solution, or in contact with the salt solution, has 
resulted from the treatment. This phenomenon was first observed by 
us in a field experiment consisting of cylinders containing a clay loam 
soil at Davis, Cal., to which solutions of sodium chloride, sulphate, 
and carbonate had been added. It will suffice here to say that the salt- 
treated soils became very impervious to water during the winter season, 
and when dry were extremely intractable. The untreated control soils 
were easily managed at all times. 
Results similar to those observed in the field were secured in the 
laboratory when sodium lactate, acetate, nitrate, chloride, sulphate, 
carbonate, and hydrate, potassium chloride, and sulphate, and ammo- 
nium sulphate were washed from the Davis soil. Magnesium chlo- 
ride is also slightly effective in the same direction, while calcium chlo- 
