146 EXTRACTION OF POTASH 



from 1854 to the present time. Quite a variety of methods are 

 indicated. The greatest number of these involve the fusion 

 process with a basic compound, usually one of the alkalis or 

 alkaline earths. Others follow a process of digestion of the 

 finely ground mineral with the same basic compounds, the time 

 factor extending from a day to a month. Electrolysis of the 

 moistened powder has also been tried but complete extraction is 

 only arrived at after many repetitions of the treatment. Others 

 have endeavored to solve the problem by heating the mineral 

 in a finely ground state to a high temperature and suddenly 

 cooling to destroy its crystalline nature, and then treating with 

 an alkali under pressure. Another method is to treat the pul- 

 verized mineral with hydrofluoric acid and treat the residue 

 with gypsum. 



A few abstracts of patents issued will give a more definite 

 idea of what has been done: 



Cushman, U. S. Pat. No. 851922, 1907, mixed powdered 

 felspar with water to form a thin sludge. This sludge was then 

 placed in a wooden container which was set inside another 

 larger vessel in which water was then placed. Electrodes are 

 introduced, the positive pole being in the inner vessel and the 

 negative in the outer. On the passage of a current, the potash, 

 soda, and other soluble bases are partially liberated and pass 

 into the water of the outer vessel. By agitating the sludge, or 

 adding thereto a small amount of hydrofluoric acid, an almost 

 complete recovery of potash is effected. 



Messerschmitt, U. S. Pat. No. 1,076,508, 1913, extracts the 

 potash from potash-bearing minerals, such as felspar, by pow- 

 dering the mineral and forming a mixture of 1000 pounds of 

 spar, 600 lbs. of basic calcium nitrate, 1 20 gallons of water, and 

 200 lbs. of lime. This mixture is introduced into a digester and 

 heated under pressure of 50-125 pounds for 10-24 hours. The 

 sludge obtained is leached with water and a solution of potassium 

 nitrate is obtained. Any calcium nitrate present is thrown down 

 by the addition of an alkali carbonate to the solution and fil- 

 tered out. The final solution is then evaporated. 



Coolbaugh and Quinney, U. S. Pat. No. 1.125,007. 1915, 

 mix felspar with gypsum or limestone, heat to fusion point, cool 

 rapidly and crush to fine powder. This powder is then leached 

 with water containing a small percentage of sulphuric acid, and 



