January 3, 19 18] 



NATURE 



345 



plants (kelp or varec) ; by the incineration of land- 

 plants (wood-ashes) ; from vinasse, or the residue 

 kft on distilling fermented beetroot molasses ; from 

 suint, or the " yolk " of sheep's wool, etc. These 

 still continue to be sources of potash, but they are 

 of comparatively subordinate importance when 

 compared with the relatively enormous output of 

 the Stassfurt deposits. All these sources, includ- 

 ing those of the Stassfurt beds, are ultimately 

 dependent on the primitive rocks of the earth — 

 that is, to the decomposition of such minerals as 

 potash felspar, potash mica, and the vast number 

 of zeolites and other silicates which make up much 

 of the rock-forming material. 



Felspars are, in fact, the most abundant mine- 

 rals in the earth's crust, constituting, according to 

 Dr. Hatch, about 48 per cent, of the whole, the 

 potash felspars forming the predominant propor- 

 tion. Orthoclase, when pure, should contain i6'9 

 per cent, of potash (KoO), but such a theoretical 

 figure is never reached, owing to a greater or less 

 admixture of soda. About 12 per cent, of potash 

 is the usual amount, which is rather more than the 

 a\erage percentage in the Stassfurt deposits. 

 Many suggestions have been made from time to 

 time to extract the potash from the two chief varie- 

 ties of potash-felspar, viz. orthoclase and micro- 

 cline, and from the intrusive igneous rock known 

 as pegmatite, which is a mixture of quartz and 

 felspar ; and a large number of patented processes 

 for this purpose are on record. It is said that up- 

 wards of one hundred patents on this subject have 

 been taken out in the United States alone. One 

 of the most promising of these was that of E. Bas- 

 sett, who, in 191 3, patented in the United States 

 and Canada a process based on the discovery that 

 powdered potash-felspar, when fritted with com- 

 mon salt, was decomposed, with the formation of 

 potassium chloride, which could be leached out 

 from the sintered material, and obtained suffi- 

 ciently pure for technical purposes by fractional 

 crystallisation. 



This process was independently discovered, and 

 has been carefully studied, by Mr. E. A. Ashcroft, 

 who has brought it to the notice of the Institution 

 of Mining and Metallurgy in a paper which has 

 just been published (Bulletin No. 159, December 

 13, 191 7). The reaction is a reversible one, and 

 for its success in affording the maximum yield of 

 potash certain conditions of fineness, temperature, 

 duration of heating, and absence of air and mois- 

 ture must be observed, which, however, would 

 seem to be easily reached in practice. Large de- 

 posits of suitable material are to be met with in 

 Gieat Britain, notably in Cornwall and in various 

 parts of Scotland and Wales. Other localities 

 occur in Ireland. Some of these are already 

 worked for pottery purposes, but others, as in 

 Sutherlandshire, on the extreme north-west coast 

 of Scotland, are untouched, and would be emin- 

 ently suitable sources of supply, and capable of 

 yielding some 20,000,000 tons of material without 

 ^oing below visible outcrops. 



Considerations of space prevent any fuller ana- 

 lysis of Mr. Ashcroft's proposals, but we are in- 

 clined to concur in his general conclusion that from 



NO. 2514, VOL. 100] 



a purely commercial point of view the attempt to 

 work these Scottish deposits seems fully justified as 

 likely to prove remunerative, and we further agree 

 with his contention that, given the raw material of 

 the pKJtash trade (the chloride), manures and all 

 other potash products can be produced at least as 

 favourably in this country as in Germany, and that 

 an important section of German trade may thus be 

 wrested from her, whilst our own urgent needs for 

 munitions of war, for the soil, and for the chemical 

 industries may be supplied. 



The Stassfurt deposits occupy an extensive basin 

 in the North German Plain, in Prussian Saxony, 

 close to the borders of Anhalt. The brine-springs 

 which they furnish have been known and inter- 

 mittently worked since the early part of the thir- 

 teenth century, but they ceased to be remunera- 

 tive, as sources of common salt, in the first years 

 of the nineteenth century, and their working was 

 abandoned. In 1839 the Prussian Mining Office 

 commenced a systematic examination of these 

 deposits, and put down a number of borings in 

 different parts of the area, with the result that the 

 potash formations were found to occur in practi- 

 cally only one locality^ near the River Bode, not 

 far from Magdeburg. During the last third of the 

 preceding century a new industry sprang up and 

 the villages of Stassfurt and Leopoldshall, from 

 being wholly insignificant places, became the 

 centres of a numerous population. 



The conditions under which the Stassfurt 

 deposits have been formed were the subject of 

 elaborate inquiry by van't Hoff and his coadjutors 

 so long as the eminent Dutch chemist lived. 

 Although his interpretation cannot be said to be 

 wholly satisfactory, the investigation greatly eluci- 

 dated the mode in which the beds are supposed 

 to occur, and rendered it very probable that similar 

 deposits will be found in other parts of the world. 

 Indeed, their existence has already been proved. 

 In 1909 large deposits of sylvine, or potassium 

 chloride, were discovered in Upper Alsace, in an 

 area of about 200 sq. km., near Mulhouse. Two 

 strata were found, the upper 3 ft. thick, the lower 

 more than i6 ft. thick at a depth of from 1600 ft. 

 to 2100 ft. This field, unlike that of North 

 Germany, seems to be continuous, without faults, 

 and is of more recent geological origin. 1 



The issue of La Nature for November 24 con- 

 tains an interesting account of what has been 

 allowed to transpire concerning these Alsatian 

 beds, from which the following particulars 

 are taken. The deposits, although continu- 

 ous, are far from being horizontal or uniform. 

 On the contrary, they are folded and irregu- 

 lar. The lower layer of sylvine is surrounded 

 and covered, throughout the whole of its 

 extent, by the upper layer, arranged somewhat in 

 the form of an ellipse, in plan not unlike, indeed, 

 a painter's palette. At the edges the saline layers 

 gradually thin out and disappear. From their 

 great depth they are naturally at a high tempera- 

 ture, not less than 48° C. From statements made 

 in 1912 it was calculated that the upper layer of 



1 Cf. Prof. Lunge in Thorpes " Dictionary of Applied Chemistry." 



