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One of the first patents on a process for converting the insoluble 

 potash in feldspar into a soluble form was issued in 1856 to Charles 

 Bickell (United States patent No. 16111). The process consists in 

 heating in a reverberatory, or other suitable furnace, to a light-red 

 heat for about 2 hours, 1 part feldspar, 0.5 part phosphate of lime, 

 and 3 or 4 parts of lime, all in a finely divided state. According to 

 the patent the potash becomes available by this treatment, and may 

 be extracted in a caustic state by lixiviating with water, or the mass 

 may be used directly as a manure. 



At first sight this process seemed particularly attractive, for . if 

 both the potash and phosphoric acid were rendered available by this 

 treatment, as claimed by the patent, the method might be an eco- 

 nomical one, since when used as a fertilizer no separation of the 

 constituents would be necessary, and the mixture would be of value 

 for its phosphoric acid as well as its potash content. 



It was found, however, that the calcium phosphate has a passive 

 effect in this treatment of the feldspar, and that no greater decom- 

 position was produced in this way than when it was heated with 

 calcium carbonate alone. 



Thus when 1 gram of feldspar, 0.5 gram of calcium phosphate, and 

 3 grams of calcium carbonate were mixed and ignited for two hours 

 at 1,000 C. in a J. Lawrence Smith crucible, the amount of potash 

 rendered soluble only amounted to about 2 per cent of the feldspar. 

 The amount of soluble potash obtained when 1 gram of feldspar 

 and 3 grams of calcium carbonate were ignited in the same way 

 likewise amounted to approximately 2 per cent, but in each case the 

 greater part of the residue remaining after extracting with water 

 was decomposed when treated with dilute hydrochloric acid, the 

 potash going into solution. 



When the temperature was increased to about 1,200 C. the soluble 

 potash amounted to 5 per cent of the feldspar, and the extracted 

 residue was then found to be readily and completely decomposed by 

 hydrochloric acid. From this solution was obtained the remaining 

 portion of the potash which did not dissolve on digesting with water. 



The crucible in which these ignitions were made was closed with a 

 cap, and as this end of the crucible was not ignited, there was little 

 tendency for the potash to escape, but when the ignition was made in 

 an open platinum dish in a furnace at a temperature of about 1,400 

 C. the potash in the feldspar was found to have been completely lost 

 by volatilization. 



In carrying out this experiment the feldspar was first dried to 

 constant weight by heating in a muffle furnace at 1,000 C. The 

 calcium oxide used was likewise reduced to constant weight by ignit- 

 ing chemically pure calcium carbonate at a temperature of 1,400 C. 



[Clr. 71] 



