MINERALS. USED AS FERTILIZERS 7I 



In the manufacture of sea-salt by evaporation in shore lagoons or 

 " saltpans," the solution remaining after the salt has been deposited 

 (known as "mother-waters," or "bittern" ), of course remains on the 

 surface of the salt unless allowed to drain off, as is done in the process 

 of manufacture. When not drained off, the water gradually evaporates, 

 and there remains a saline crust of a composition exactly resembling 

 that of the upper layers at Stassfurt, containing a large proportion of 

 potash salts. 



If it be asked why the Stassfurt salts are not found overlying every 

 rock-salt deposit in the world, the answer is that in a great many cases 

 the concentrated mother-waters have had an opportunity to flow off 

 from the surface of the rock-salt by the action of tides, the inflow of 

 fresh water from the land or from other causes. Their presence 

 therefore depends upon the fulfilment of accidental conditions not 

 nearly always realized in the natural evaporation of sea-water, but 

 which happened to occur on a very large scale in that portion of the 

 North-European continent. 



Nature of the Salts. -The potash is present in the Stassfurt salts in 

 the form of complex sulfates and chlorids containing, besides, sodium, 

 calcium and magnesium in various proportions and modes of com- 

 bination. The most abundant of the potassic chlorid minerals is car- 

 nallite, a hydrous chlorid of potassium and magnesium. The chlorids 

 characterize chiefly the upper portions of the deposit, the sulfates 

 the lower. 



Kainit. Of the products derived from the Stassfurt salt 

 industry for agricultural use, the two requiring special con- 

 sideration are " kainit," a natural mixture of the several chlo- 

 rid minerals in varying proportions; and "high-grade sul- 

 fate." Being a natural product, " kainit " is the cheapest 

 source of potash available to the farmer; but on account of 

 its variability in composition it must be sold and purchased on 

 guaranteed assay. On account of its large content of chlorin 

 it is not desirable in the production of certain crops, especially 

 in 'the arid region, where alkali soils, and even those not visi- 

 bly alkaline, often contain already large amounts of chlorin. 

 Moreover, kainit usually contains a considerable proportion 

 of common salt. For the arid region therefore the sulfate 

 is generally preferable, although it is somewhat higher in 

 price for the same amount of potash. The potash content of 



