234. The Destruction of Organic Matter by Moist Combustion.—In the process of ignition to destroy organic matter or remove ammonium salts in the determination of potash, there are often sources of error which may cause considerable loss. This loss, as has already been mentioned, may arise from the volatilization of the potash salts or mechanically from spattering. In order to avoid these causes of error de Roode has used aqua regia both for the destruction of the ammonium salts and for the oxidation of the organic matter at least sufficiently to prevent any subsequent reduction of the platinum chlorid.[193] His method consists in boiling a sample of the fertilizer, or an aliquot portion of a solution thereof with aqua regia. The proposed method has not yet had a sufficient experimental demonstration to warrant its use, but analysts may find it profitable to compare this process with the standard methods. The organic matter may also be destroyed by combustion with sulfuric acid, as in the kjeldahl method for nitrogen. The residue, however, contains ammonium sulfate and a large excess of sulfuric acid, and for both reasons would not be in a fit condition for the estimation of potash.
It is suggested that the organic matter might also be destroyed by boiling with strong hydrochloric acid, to which from time to time, small quantities of sodium chlorate free of potash is added. Subsequently the solution could be boiled with addition of a little nitric acid and the ammonium salts be removed.
POTASH IN MINERAL DEPOSITS.
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.
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: