AGRONOMY: L. T. SHARP 
567 
which salts have been added. Obviously this would be the case when 
we are considering suspensions of the soil mass in various solutions. 
Some doubt, however, may be expressed as to the vaHdity of this state- 
ment when a soil of normal moisture content is compared to the dis- 
persoid of a disperse system, or to a soil suspended in a liquid. For 
in the normal soil such factors as the surface tension of the liquid-air 
surface may be of such magnitudes as to materially alter conditions 
so that the laws referred to would not be applicable to such systems. 
In order to see how far the analogy can be drawn let us consider, for 
example, clay. Clay has been shown to be a lyophobic colloid which 
assumes the negative charge of OH ions when suspended in water. 
The addition of more OH ions as by NaOH within certain limitations 
lowers the solid-liquid surface-tension so that a greater diffusion results. 
If a positive ion is added to the system, the OH ions are neutralized, 
the surface-tension increases, and the clay particles increase in size until 
they finally settle to the bottom of the vessel. So far the well known 
facts agree with the theory and, moreover, it is evident that the nature 
of the medium of suspension is an important factor. When a salt, such 
as sodium chloride, is added to a soil and subsequently leached out, it 
may be possible that the medium of suspension has been materially 
altered. The selective adsorption of the sodium by the soil may eventu- 
ally give rise to OH ions, in which case the soil would become more or 
less diffused. By means of the hydrogen electrode we have been able 
to obtain specific data with respect to the quantity of OH ions present 
in the medium of suspension. Our results so far indicate that there 
is not a sufficient quantity of OH ions in the solution bathing the soil 
particles of the salt treated soil, to account for its unusual degree of 
diffusion. These data bear significantly on the general behavior of the 
soil suspension under various conditions. 
If a soil which has been previously treated with salt and leached 
with water is subjected to drying at 130° C, it loses only a small por- 
tion of its diffusible colloidal material. Whatever other bearing this 
may have upon the subject, it at least indicates that the change is of a 
permanent character. 
In the course of these investigations we have also noted that salt 
solutions of low concentration (less than r^V-cr normal) have little or no 
effect on a soil suspension, so that the mere dilution of the salt solutions 
can not account for the effects observed. Moreover, it has been found 
that it is not necessary to wash the soil entirely free from salt in order 
to produce the defiocculated condition. 
One other interesting observation with respect to the difference in 
behavior of sodium hydroxide and carbonate came to our notice. Sodium 
