POTASSIC MANURES 119 



granted; nor is it at all likely in view of the 

 comparatively low percentage of potash in all 

 silicate rocks that any process can be devised 

 which will prove so simple that the value of the 

 potash alone will pay for its extraction. So far 

 as I ani informed these processes have never been 

 practical on account of the fact that in all of 

 them the cost of producing the potash is greater 

 than its market value. It may be that on account 

 of the European War some of these processes will 

 become commercially feasible. It seems safe to 

 say, therefore, that any method to be economical 

 must produce at the same time other products 

 of value in addition to the potassium. 



In a modification of the old Charles Bickell 

 process, it has been shown that all the corstitu- 

 ents of pure feldspar-lime clinker lie between the 

 limits allowable in a good Portland cement, and 

 that ferric oxide is the only necessary constituent 

 absent. If commercial feldspar and lime were 

 used, however, this would no doubt also be sup- 

 plied in sufficient quantity, and at the same time 

 the silica and lime would be reduced more closely 

 to the mean of that found in good Portland cement, 

 providing the feldspar does not contain an exces- 

 sive amount of free silica. 



In order that a clay may be suited for the manu- 

 facture of cement it should have a percentage ratio 

 of silica to alumina of from 3 to 1 or 4 to 1. The 

 ratio of these two constituents in feldspar is 

 3,5 to 1. In muscovitc and leucite of theoretical 



