POTASSIC MANURES 115 



bearing material containing mica by essentially 

 the same treatment as that covered by Rhodin's 

 patent for the extraction of potash from feldspar. 

 United States Patent No. 987,436 was granted 

 to A. S. Cushman in 1911 for a method for ob- 

 taining potash from silicate rocks. According 

 to this method the feldspathic rock is reduced 

 to as fine a subdivision as possible and mixed 

 with finely powdered quicklime in the proportion 

 of 100 parts of the rocks to 20 parts of lime. 

 The mixture is then spread on a suitable con- 

 veyor, as belt or drum, in the form of a bed 

 having a thickness from three-eighths to one- 

 half inch. To the surface of this bed is applied 

 a solution of calcium chloride in separate drops 

 and of such a concentration that the amount of 

 calcium chloride added should be sufficient to 

 supply chlorine in quantities at least molecularly 

 equivalent to the total alkali contained in that 

 portion of the feldspar which becomes aggre- 

 gated into lumps on the addition of solution. 

 The aggregates which harden quickly at or- 

 dinary temperatures, are separated from the un- 

 converted powder by screening, and then heated 

 in a rotary kiln at a temperature preferable, 

 but not necessarily, below the point at which 

 a substantial part of the potassium chloride is 

 sublimed. The product is discharged contin- 

 uously from the furnace in lumps and may be 

 crushed for use directly as a fertilizer; or the 

 potassium chloride may be extracted by means 



