POTASH 593 



We find next the region of polyhalite, still composed of rock-salt, but intersected by 

 veins of 2 to 3 c.m. thick, formed of polyhalite, a mineral composed of the sulphates of 

 lime, magnesia, and potash. This layer is about 64 meters in thickness, and is com- 

 posed on an average of 91 -2 per cent, chloride of sodium, 0*66 of karstenite, 6'63 of 

 polyhalite, and 1'51 of hydrated chloride of magnesium. 



To this stratum succeeds another of a different composition, and characterised by 

 the presence of a saline mineral named kieserite. It consists of mono-hydrated sul- 

 phate of magnesia, in small microscopic needles. The layer contains 65 per cent, of 

 chloride of sodium, 1 7 of kieserite, 1 3 of carnallite, 3 of chloride of magnesium, and 2 

 of karstenite. Its thickness is 56 meters. The upper region is formed of a group of 

 salts chiefly magnesic and potassic, and formerly called riddance salts (Abraumsalze), 

 because they were at first without industrial application, and were merely extracted to 

 reach the rock-salt below. These salts are now the foundation of the trade of Stassfurt. 

 The principal salt is carnallite, a chloride of potassium and magnesium. It has a red 

 colour, due to the presence of oxide of iron in microscopic lamellae. There are found 

 also in this deposit sylvine and Howellite, a chloride of potassium containing often small 

 quantities of sulphate of potash, and of sulphate and chloride of magnesium ; tachyhy- 

 drite, a carnallite in which the chloride of potassium is replaced by chloride of calcium ; 

 and boracite, a combination of the borate and chloride of magnesium. Stassfurt, as we 

 have stated, lies on the Prussian frontier, towards the borders of the Duchy of Anhalt. 

 The Prussian workings, therefore, could not be extended to the south-west, where the 

 geological conditions were most favourable. In 1855 the Government of Anhalt com- 

 menced operations within its own territory, with perfect success. The saline beds 

 were reached at the depth of 145 meters, and soon a new salt was discovered in great 

 quantity, giving a new impulse to the trade of the district. This is kainite, a 

 compound of sulphate of magnesia and chloride of magnesium. Its discovery enabled 

 the inhabitants to enter upon the manufacture of pure sulphate of potash, which is 

 largely exported to England and the United States. Their applications are numerous. 

 The chloride of potassium is used in the manufacture of saltpetre and carbonate of 

 potash; the sulphate of potash is in great dema'nd in the glass and alum works. 

 Stassfurt exports also sulphate of magnesia and chloride of magnesium, which are 

 extensively used in England for the discreditable purpose of adding to the weight of 

 textile goods, and rendering them hygroscopic ; bromine to an extent almost sufficient 

 for the consumption of Europe, and boracic acid. Lastly, the impure salts obtained 

 as waste in the various refining processes, consisting principally of salts of soda, 

 magnesia, and potash, are skilfully combined, and sold as mineral manures, more or 

 less rich in potash and magnesia. The demand for these manures has greatly in- 

 creased of late years, especially in England and Germany. In 1869 the Prussian mine 

 alone yielded 109,075,000 kilos of salts of potash, and 56,332,000 kilos of rock-salt, 

 representing a total value of 916,960 francs. It is interesting to note that whereas 

 the application cf potassic salts in agriculture, some fifteen or twenty years ago, 

 was found to produce little or no benefit, they are shown by more recent experiments 

 to be highly valuable. Liebig has shown that the use of manures which contain only 

 some of the ash-constituents of the crops merely enables the soil to be more rapidly 

 exhausted of the other necessary constituents. See CABNALLITE; KAINITE; KIESERITE; 

 SYLVINE. 



Caustic potash, after being fused in a silver crucible at a red heat, retains 1 equi- 

 valent of water. Hence its composition in 100 parts is, potassium 70, oxygen 14, 

 water 16. Anhydrous potash, or the oxide free from water, can be obtained only by 

 the oxidation of potassium in air. It is composed of 83^- of metal and 16| of oxygen. 



Caustic potash may be crystallised ; but in general it occurs as a white brittle sub- 

 stance of spec. grav. 1'708, which melts at a red heat, evaporates at a white heat, 

 deliquesces into a liquid in the air, and attracts carbonic acid ; is soluble in water and 

 alcohol, forms soft soaps with fat oils, and soapy-looking compounds with resins and 

 wax ; dissolves sulphur, some metallic sulphurets, as those of antimony, arsenic, &c., 

 as also silica, alumina, and certain other bases ; and decomposes animal textures, as 

 hair, wool, silk, horn, skin, &c. It should never be touched with the tongue or the 

 fingers. 



The only certain way of determining the quantity of free potash in any solid or 

 liquid is from the quantity of a dilute acid of known strength which it can saturate. 



The hydrate of potash or its lye often contains a notable quantity of carbonate, the 

 presence of which may be detected by lime-water, and its amount be ascertained by 

 the loss of weight which it suffers, when a weighed portion of the lye is poured into a 

 weighed portion of dilute sulphuric acid poised in the scale of a balance. 



The following Table exhibits the quantity of potash in 100 parts of caustic lye, at 

 the respective densities ; 



VOL. III. Q Q 



