4 BULLETIN 143, U. S. DEPARTMENT OF AGRICULTURE. 



of the minerals and the expense of collecting and recovering the 

 potash and phosphoric acid thus violatilized make it very doubtful 

 if this process is commercially practicable. 



THE FUSION OF FELDSPAR AND PHOSPHATE ROCK. 



The solubility of phosphates in certain organic solutions has for a 

 long time been regarded as a test of their agricultural availability. 

 The nature and strength of the organic solvent used differs in various 

 countries, and since each process is based on an arbitrary standard, 

 it can only give corresponding results when conditions are the same. 

 But in spite of the fact that none of these methods is founded upon 

 a strictly scientific basis, it is generally thought that phosphates 

 soluble in such solutions are under soil conditions more active than 

 those which do not dissolve in the same mediums. 



The beneficial effect of the phosphoric acid in finely ground 

 steamed bone is unquestioned, and although little of it is water 

 soluble, a neutral solution of ammonium citrate will dissolve from 

 12 to 31 per cent of the acid, depending on the temperature of the 

 solution and the time of contact. 1 It is also an indisputable fact 

 that excellent results have been obtained bv the use of basic slag as 

 a fertilizer, and it is claimed that these results are commensurable 

 with the amount of citric soluble phosphoric acid present in the 

 material. 



It has therefore become customary to regard citrate or citric 

 soluble phosphoric acid as having a commercial value nearly equal 

 to that of water soluble phosphate. 2 While this is true of phos- 

 phates, the same view is not taken of potash-bearing substances, 

 since practically all of the potash carriers used in agriculture are 

 water soluble. The potash in the ordinary soil minerals is almost 

 entirely insoluble in water, and but slightly soluble in the mineral 

 acids, but if the potash present could be converted into a citric 

 soluble form there seems to be no reason why it should not be con- 

 sidered as available to crops as citric soluble phosphoric acid. 



During some investigations carried on in this laboratory on the 

 possibilities of rendering the slags from the iron and steel industries 

 available for fertilizer purposes, 3 attempts were made to fuse to- 

 gether mixtures of feldspar and phosphatic limestone with a view to 

 obtaining both the potash and phosphoric acid present in an " avail- 

 able " form. Mixtures containing various proportions of these two 



1 Huston, H. A., 32d Annual Report Indiana State Board of Agriculture, p. 230 (1883) ; 

 Wiley, II. W., Principles and Practice of Agricultural Analysis, vol. 2, p. 47 ; Wheeler, 

 H. .1., Manures and Fertilizers, p. 172 (1913). 



2 A report of a conference of the experiment stations of New York, New Jersey, and 

 New England, Mar. 1, 1911, indicates that citrate soluble phosphoric acid has about 

 nine-tenths of the fertilizer value of water soluble phosphoric acid. 



3 Bui. 95, Bureau of Soils, U. S. Dept. of Agr., 1912. 



