66 4 
Journal of Agricultural Research 
Vol. XXVII, Nor 9 
turbidity of the water extract, and in cementation on drying. When 
the preponderance of combined bases is with the alkaline group the soil 
is less permeable to water, the soil extract is more turbid, and the soil 
tends to cement together on drying. When the preponderance is with 
the elements of the earthy group these symptoms are manifested in the 
opposite direction. 
It should be kept in mind that the full development of these symptoms 
in the direction of the alkaline response does not take place while the 
soil solution contains large quantities of the stronger acid electrolytes, 
such as chlorin, sulphate, or nitrate. In other words, the presence, of 
these acid electrolytes in the solution tends to prevent the manifesta¬ 
tion of the physical effects that follow the replacement of the earthy 
bases by the alkaline bases in the soil combination. The removal of 
these dissolved acid ions by leaching the soil or the dilution of the soil 
solution permits the physical effect of the combination of the alkaline 
bases with the soil to be shown. 
The replacement by an alkaline base of the earthy bases combined 
with the soil and the effect of this exchange on the permeability of the 
soil may be observed by following the course of events in a simple leach¬ 
ing experiment. In such an experiment a soil of good permeability should 
be used. It should be treated with sodium chlorid or sodium sulphate 
or leached for a time with a solution of one of these. It should then 
be leached with distilled water to remove the acid electrolyte from 
the soil solution. An examination of the percolates obtained from the 
leachings with the salt solution will show that these differ from the 
solution applied to the soil in that they contain less sodium and that this 
decrease in sodium is made up by other bases, chiefly calcium. After the 
leachings with distilled water are begun the percolates become more 
dilute and the percolation rate becomes much slower and may cease 
altogether. 
The same physical condition of the soil that makes for impermeability 
to water is also shown by increased turbidity of the water extract of the 
soil. This may be demonstrated by taking a small quantity of soil 
used in the leaching experiment just described and shaking it up with 
water. The use of io parts of water to i part of soil gives a good example. 
Another sample of soil taken after the leaching experiment is completed 
and treated with water in the same way shows the contrast in the turbid¬ 
ity of the extract. These differences in turbidity of the water extract 
of a sample of salty soil before and after leaching are shown in figure 6. 
Each of the tubes shown in the figure contained 5 gm. of soil and 50 cc. 
of water. After the mixture was thoroughly shaken, the tubes stood for 
two days before the photograph was made. In the tube at the right 
which contained the unleached soil the solution cleared within a few 
minutes. In the other tube only the larger particles settled out, the 
fine material remaining suspended in the solution. 
The differences in the cementation properties of a soil in which the 
earthy bases have been replaced by an alkaline base may be shown by 
drying a sample from the leaching experiment described above and 
comparing it with a sample of the original soil that has been saturated 
but not leached. Such comparison shows that the alkaline treated soil 
becomes harder on drying than the original permeable soil. 
