=235. Occurrence and History.=—The generally accepted theory of the
manner in which potash has been collected into deposits suited to
use as a fertilizer has already been described.[194] The Stassfurt
deposits, which have for many years been almost the sole source of
potash in fertilizers, were first known as mines of rock salt. In
1839, having previously been acquired by the Prussian treasury, they
were abandoned by reason of the more economical working of rock salt
quarries in other localities.[195] It was determined thereafter to
explore the extent of these mines by boring, and a well was sunk to
the depth of 246 meters, when the upper layer of the salt deposit was
reached. The boring was continued into the salt to a total depth of 581
meters without reaching the bottom. The results of these experiments
were totally unexpected. Instead of getting a brine saturated with
common salt, one was obtained containing large quantities of potassium
and magnesium chlorids.[196] Shafts were sunk in other places, and with
such favorable results, that in 1862 potash salts became a regular
article of commerce from that locality. At first these salts were
regarded as troublesome impurities in the brine from which common
salt was to be made, but at this time the common salt has come to be
regarded as the disturbing factor. At the present time the entire
product is controlled by a syndicate of nine large firms located
at Stassfurt and vicinity. Outside of the syndicate properties a
shaft has been sunk at Anderbeck, (Halberstadt,) which, however, has
produced only carnallit, since kainit has not been found there. Also
at Sondershausen, potash salts have been discovered and a shaft is now
sinking there.
It is thus seen that the potash deposits extend over a wide area in
Germany, and there is little fear of the deposits becoming exhausted in
many centuries. In this country no potash deposits of any commercial
importance have been discovered; but the geological conditions
requisite to these formations have not been wanting, and their future
discovery is not improbable.
[Illustration: FIGURE 17. GEOLOGICAL RELATIONS OF THE POTASH
DEPOSITS NEAR STASSFURT.]
=236. Changes in Potash Salts in Situ.=—The deposits of potash salts
are not all found at the present in the same condition in which they
were first deposited from the natural brines. The layers of salt have
been subjected to the usual upheavals and subsidences peculiar to
geological history. The layers of salt were thus tilted and the edges
often brought to the surface. Here they were exposed to solution, and
the dissolved brine afterward separated its crystallizable salts in
new combinations. For instance, kieserit and the potassium chlorid of
the carnallit were first dissolved and there was left a salt compound
chiefly of potassium and sodium chlorids, sylvinit. In some cases
there was a mutual reaction between the magnesium sulfate and the
potassium chlorid and the magnesium potassium sulfate, schönit, was
thus produced. This salt is also prepared at the mines artificially.
The most important of these secondary products however, from the
agricultural standpoint, is kainit. This salt arose by the bringing
together of potassium sulfate, magnesium sulfate, and magnesium
chlorid, and was formed everywhere about the borders of the layers of
carnallit wherever water could work upon them. In quantity the kainit,
as might be supposed, is far less than the carnallit, the latter
existing in immense deposits. There is however quite enough of it to
satisfy all the demands of agriculture for an indefinite time. In fact
for many purposes the carnallit can take the place of kainit without
detriment to the growing crops. The relative positions and quantities
of the layers of mineral matters in the potash mines, and the depth in
meters at which they are found is shown in Fig. 17.[197]
=237. Kainit.=—The most important of the natural salts of potash for
fertilizing purposes is the mixture known as kainit. It is composed
in a pure state of a molecule each of potassium sulfate, magnesium
sulfate, magnesium chlorid, and water. Chemically it is represented by
the symbols:
K₂SO₄·MgSO₄·MgCl₂·H₂O. Its theoretical percentage of potash (K₂O),
oxygen = 16, is 23.2.
Pure kainit, however, is never found in commerce. It is mixed naturally
as it comes from the mines with common salt, potassium chlorid, gypsum,
and other bodies. The content of potash in the commercial salt is
therefore only a little more than half that of the pure mineral. In
general it may be taken at 12.5 per cent, of which more than one per
cent is derived from the potassium chlorid present. The following
analysis given by Maercker may be regarded as typical:[198]
Potassium sulfate 21.3 per cent
Magnesium “ 14.5 “
Magnesium chlorid 12.4 “
Potassium “ 2.0 “
Sodium “ 34.6 “
Calcium sulfate (gypsum) 1.7 “
Water 12.7 “
Alumina 0.8 “
Kainit occurs as a crystalline, partly colorless, partly yellow-red
mass. When ground, in which state it is sent into commerce, it forms a
fine, gray-colored mass containing many small yellow and red fragments.
It is not hygroscopic and if it become moist it is due to the excess of
common salt which it contains.
According to Maercker kainit was formerly regarded as a potassium
magnesium sulfate. But this conception does not even apply to the pure
salt much less to that which comes from the mines. If, therefore, the
agronomist desire a fertilizer free from chlorin he would be deceived
in choosing kainit which may sometimes contain nearly fifty per cent of
its weight of chlorids.
Where a fertilizer free of chlorin is desired, as for instance, in the
culture of tobacco, kainit cannot be considered. In many other cases,
however, the chlorin content of this body instead of being a detriment
may prove positively advantageous, the chlorids on account of their
easy diffusibility through the soil serving to distribute the other
ingredients.
By reason of the presence of common salt and magnesium chlorid the
ground kainit delivered to commerce tends to harden into compact
masses. To prevent this in Germany it is recommended to mix it with
about two and a half per cent of fine-ground dry peat.
Such a mixture is recommended in all cases where the freshly ground
kainit is not to be immediately applied to the soil.
=238. Carnallit.=—This mineral is a mixture of even molecules of
potassium and magnesium chlorids crystallized with six molecules of
water. It is represented by the symbols KCl·MgCl₂·6H₂O. As it comes
from the mines it contains small quantities of potassium and magnesium
sulfates and small quantities of other accidental impurities. Existing
as it does in immense quantities it has been extensively used for the
manufacture of the commercial potassium chlorid (muriate of potash).
For many purposes in agriculture, for instance, fertilizing tobacco
fields, it is not suited, and it is less widely used as a fertilizer
in general than its alteration product kainit. Its direct use as a
fertilizer however is rapidly increasing since later experience has
shown that chlorin compounds are capable of a far wider application
in agriculture without danger of injury than was formerly supposed.
As it comes from the mines, the Stassfurt carnallit has the following
composition:[199]
Potassium chlorid 15.5 per cent.
Magnesium “ 21.5 “ “
Magnesium sulfate 12.1 “ “
Sodium chlorid 22.4 “ “
Calcium sulfate 1.9 “ “
Water 26.1 “ “
Undetermined 0.5 “ “
Pure carnallit would have the following composition:
Chlorin 38.3 per cent.
Potassium 14.0 “ “
Magnesium 8.7 “ “
Water 39.0 “ “