12 BULLETIN" 312, U. S. DEPARTMENT OF AGRICULTURE. 



The processes of Schlutius 1 and Bretteville, 2 in which nitric acid 

 is employed as a solvent instead of sulphuric acid, are of interest 

 because calcium nitrate and soluble calcium phosphate are produced, 

 both of which are fertilizer materials. 



Ca 3 (P0 4 ) 2 +4HN0 3 =CaH 4 (P0 4 ) 2 +2Ca(N0 3 ) 2 . 



Such a mixture is sufficiently high grade to stand the expense of 

 long shipment, but the well-known hygroscopic properties of calcium 

 nitrate form a drawback to its use in fertilizers and would probably 

 necessitate shipping the material in air-tight containers. 



PROCESSES FOR THE PRODUCTION OF PHOSPHORIC ACID OR SOLUBLE 

 PHOSPHATES BY COMBINED HEATLNG AND ACID TREATMENT. 



In general, these processes are not very promising, since they 

 involve both acid treatment and the expense of heating the product. 

 A list of the patents under this head is given in Table IV, Appendix. 



The process of Scribner 3 appears to be of much interest. It con- 

 sists in either roasting a mixture of phosphate rock and sulphur or 

 passing sulphur dioxide over highly heated phosphate rock. In 

 either case it is claimed that citrate-soluble phosphate results. 



This scheme is similar to two described under "Acid treatment." 

 If it accomplishes what is claimed, much unnecessary time and 

 expense may be saved in the manufacture of available phosphates. 

 From the experience in the Bureau of Soils laboratories, however, it 

 would seem rather difficult to conduct this process so as to effect the 

 complete conversion of the phosphoric acid into an available form. 



This patent expired in 1900. 



DOUBLE DECOMPOSITION BY MEANS OF AN ALKALI, AN ALKALI SALT, 



OR ALKALINE EARTH. ' 



All the processes under this head except four depend on heat to 

 effect the conversion of insoluble phosphate into a water-soluble or 

 citric-soluble form. In Table V, Appendix, a list of the various 

 patents on this subject is given. 



The object of the processes described below is to obtain a neutral 

 or alkaline product containing available phosphoric acid. Owing 

 to the acid properties of superphosphate there exists among certain 

 farmers considerable prejudice against its use. Fertilizers of the 

 type described below have, as a rule, an alkaline reaction, and there- 

 fore are popularly believed to counteract any acidity in the soil. 



In the process of Commins, 4 phosphate rock is either heated to 

 redness and then saturated with a solution of sodium chloride or 

 first treated with the salt solution, heated, and then plunged into 

 gas-house liquor. In the more recent process of Lowman, 5 a mixture 



i United States Patent No. 872757 (1907). * United States Patents Nos. 74799, 78061 (1868). 



2 United States Patent No. 1011909 (1911). 5 United States Patent, No. 922494 (1909). 



a United States Patent No. 283426 (1883). 



