109 
southern soils. These amounts are computed in round numbers on the baais of 
3,000,000 pounds as the mean weight of an acre-foot of dry soil, whereas the actual 
mean weight of the surface 4 feet is very nearly 4,000,000 pounds. The amounts 
given, therefore, are considerably under the absolute values. 
In another series of determinations of the surface fool only, covering six different 
periods, the mean total salts recoverable by three-minute washings in distilled water 
were 482.45 parts per million of the dry soil as a mean for the two northern areas, 
and 192.73 parts per million for the two southern areas, making the amount from 
the northern soils 2.48 times that from the southern soils. 
Taking the dry weight of the surface foot at only 2,000,000 pounds, which is much 
less than the lightest soil, the soil moisture of the surface foot carries more than 965 
pounds per acre at the North as against 385 pounds per acre for the South. 
From several lines of evidence it has been demonstrated that a three-minute wash- 
ing of soils in distilled water, which we have adopted arbitrarily as a matter of con- 
venience for our comparative studies, does not recover all of the water-soluble salts 
which are present in these soils. In order to form some idea of how large amounts 
of water-soluble salts may be recovered by repeated washing in distilled water, two 
series of observations have been made by repeatedly washing the same sample in 
distilled water eleven consecutive times, with alternate drying of the samples between 
each washing. With this treatment applied to the eight soil types under compari- 
son, there were recovered from the surface foot alone of the northern soils at the 
rate of 699 pounds of potash (expressed as K) against 613 pounds from the southern 
soils. Of lime, there were recovered 2,179 pounds from the northern and 512 pounds 
from the southern. Of magnesia, 873 pounds from the northern as against 290 
pounds from the southern. Of nitrates, 431 pounds from the northern as against 
211 pounds from the southern. Of phosphates (expressed as HP0 4 ), 984 pounds 
from the northern as against 408 pounds from the surface foot of the southern soils, 
and of S0 4 , the amounts stand 1,800 pounds from the northern to 736 pounds from 
the surface foot of the southern soils. 
To make sure that such differences as these were not accidental, or mere coinci- 
dences, there have been brought together into comparison live independent series of 
determinations, three of which represent the amounts recoverable by single three- 
minute washings, while the other two combine the amounts recovered by eleven 
repeated washings of the same sample. Two of the three sets of results obtained from 
the three-minute washings are averages of long series of observations, while the other 
one is a single series of determinations made on a set of composite samples composed 
of a large number of soil cores. So, too, with the two series of eleven-times-washed 
soils. These are single determinations made on composite samples of many cores. 
When the total water-soluble salts recovered from these five series are compared, 
taking the amounts recovered from the southern soils as 1 in every case, the ratios 
stand: 2.22 to 1, 2.48 to 1, 2.09 to 1, 2.37 to 1, and 2.78 to 1, the last two ratios being 
the eleven-times-washed soils. 
It must be clear, I think, from the ratios found for these two groups of soils that 
there is a real difference between them expressed by the ratios; and that, if the abso- 
lute amounts of water-soluble salts in these two groups of soils are not in the ratios 
represented, then the amounts which can be washed out from the soils by using dis- 
tilled water, as has been done, are represented by the ratios. 
Taking the mean value of these ratios, the total amounts of recoverable water-sol- 
uble salts by the methods used stand 2.39 for the northern soils to 1 for the south- 
ern, while the mean yields of corn and potatoes from these two groups of soils, 
expressed in bushels, stand, possibly as a mere chance, very nearly in the same ratio, 
namely, 2.47 to 1. 
When the process of washing in distilled water is reversed and a solution of known 
salts is passed through the soils by percolation, or they are simply brought in contact 
with the solution, the different soils have markedly different effects upon the solu- 
tion, retaining the ingredients of the solution in varying amounts. 
In one series of observations on the eight soil types under investigation, after sam- 
ples of them had been eleven times washed in distilled water by percolation, there 
was passed through the same samples three times in quick succession a quantity of a 
solution equal to five times the dry weight of the soil which carried 300 parts per 
million of K in solution, 340 parts of lime, 300 parts of magnesia, 470 parts of NO s , 100 
parts of HP0 4 , and 1,600 parts of S< ) A , the salts used being calcium phosphate ( CaH I'O, ) 
calcium nitrate, potassium sulphate, and magnesium sulphate. It was found, after 
passing this solution three times through the eight soil types, that they had retained, 
as a general average for the eight soils, 427 parts per million of their dry weight of 
K, 660 parts per million of Ca, 753 of Mg, 269 of NO s , 120 of HP0 4 , and 1,032 of 
S0 4 . Even a freshly powdered granite, composed of orthoclase-feldspar, quail/, and 
muscovite mica, removed from the same solution 230 parts per million of its dry 
