4 
Colorado Experiment Station 
most of our soils the alkali will show if a sample of wet soil be allowed 
to dry slowly, when perhaps the whole surface, or possibly certain 
prominences, will become white. This is a sufficient amount to justify 
one in considering the soil as carrying alkali. It is evident that this 
applies to “white alkali” alone; “black alkali” will betray its presence 
in other ways, the principal of which is the tendency of the soil to be¬ 
come very hard and to turn black where any drops of water may ooze 
out of it. 
The salts present in these alkalis are the sulfate of soda, (Glauber’s 
salt), the sulfate of lime (gypsum), and sulfate of magnesia (Epsom 
salts), sodic chlorid (common kitchen salt), sodic carbonate (ordinary 
washing soda), and possibly, also, sodic bicarbonate (baking soda). 
Sometimes we have still other salts, calcic, magnesic, and sodic nitrates, 
also calcic chlorid, etc. In some alkalis we find small amounts of potas- 
sic salts and phosphoric acid. These, together with substances that oc¬ 
cur rarely or always in small quantities, we may neglect. 
The origin of the sulfates, chlorids and carbonates can be traced 
directly to the minerals in the soil. So far as the sulfates are con¬ 
cerned we have an abundant supply of them in the minerals themselves. 
For instance, felspar contains sulfuric acid, chlorin and phosphoric acid 
enough to supply a very great quantity of sulfates in the form of 
gypsum or of sodic sulfate. We do not need this source for we have a 
great supply of sulfate in the gypsum which is very common in Colo¬ 
rado, and which is very often present in the marl or hard pan that has 
formed in nearly all of our lands. In some places the sulfid of iron, 
marcasite, and pyrites may form by their oxidation sulfuric acid and 
sulfates which eventuallv give rise to the sulfates of soda, lime or 
magnesia. 
SULFATES AND CHLORIDS CONSIDERED “WHITE ALKALI”, SODIC 
CARBONATE “BLACK ALKALI” 
Of these salts usually found in the alkalis the sulfates with the 
chlorids are considered as “white alkali”. The salts are themselves 
white and the water in and on the land where they occur is only slightly 
if at all colored. Sodic carbonate is called “black alkali”, not because 
the salt is black, for washing soda and baking soda are white salts, but 
the solutions of washing soda in the soil where there is a lot of half 
decomposed plant or vegetable matter dissolves this half decomposed 
stuff to a black solution. This salt, or its solution is, moreover, so 
caustic that, if it be kept, especially strong solutions of it, in contact 
with the stems of plants, it will eat them, that is, destroy their tissues 
and kill them. The vegetable matter and the solution of the salts at 
the same time becoming black. In this way it has come to be called 
“black alkali”. 
