The Soil. 
41 
These analyses are sufficient to show how very different the 
percentages of the various salts are in the alkali, and in that portion 
of the soil which is soluble in water. The latter contains a rela¬ 
tively small amount of sodic sulfate, the former a large amount. 
The sodic sulfate, together with the magnesic sulfate, is concen¬ 
trated in the alkali. 
FORMATION OF ALKALI INCRUSTATIONS EXPLAINED. 
§ 82. The formation of these incrustations effects a rough sep¬ 
aration of the markedly efflorescent salts, sodic and magnesic sul¬ 
fates, from the permanent calcic sulfate. Ordinary salt, sodic 
chlorid, which is present, is also concentrated in the alkali, but not 
nearly to a like extent, as those already named. The highest figure 
obtained for the sodic sulfate in any sample of the water-soluble is 
in the first two inches of soil designated as B, in which it amounts 
to 27 per cent. In the alkalies it is practically 54 per cent., or twice 
as much. The highest percentage of magnesic sulfate in the water- 
soluble is 24 per cent., found in the first two inches of the soil C, 
while the average for the two samples of alkali is 28 per cent. The 
•decrease of the calcic sulfate from the amount present in the water- 
soluble to that present in the alkali, is more marked than the in¬ 
crease in the sodic sulfate in the alkali given above. The mini¬ 
mum of the calcic salt found in the water-soluble is 34 per cent., the 
maximum 67 per cent., while the amount in these alkalies are 7.5 
and 3.3 per cent., respectively. These relations show us the deport¬ 
ment of these salts when present in the soil solutions, whose surfaces 
are brought up and exposed to the evaporating influences of the at¬ 
mosphere and sun. It is quite a different matter when the free 
surface of the water in lakes and ponds is presented to the same. 
In this case there is simply an evaporation to dryness, and 
the residue represents the salts held in solution by the waters, 
whereas, in the efflorescing alkalies we have the chemical and phys¬ 
ical properties of these salts playing an important, if not the most 
important part. The sodic sulfate is predominant in the alkali, 
not because there is more of it in solution in the soil, but because it 
is separated more readily at the surface of the solution than the cal¬ 
cic sulfate. Magnesic sulfate also passes out of the solution more 
readily than the calcic sulfate, not because there is more of it in the 
solution, but because its chemical properties are different and its de¬ 
partment toward the dissolving water and the soil particles is dif¬ 
ferent. This subject will be discussed more fully and tacts given, 
when we consider the soil waters. I wish, however, to emphasize 
the fact that the efflorescent alkalies are quite different from the resi¬ 
dues left by evaporating bodies of water; such residues seem to be 
intermediate between those obtained by evaporating grouud waters 
to dryness and the salt brought to the surface by capillarity and 
separated as efflorescences on the ground. 
