PHOSPHATE KOCK: UTILIZATION AS FERTILIZER. 13 



of phosphate rock, sodium chloride, dolomite, and fluorite is made 

 into a paste with water and then baked for 12 hours at 700° F. The 

 inventor claims that citrate-soluble phosphoric acid results, but states 

 that he does not know what reactions take place. 



Considering the materials used, however, it is probable that a more 

 basic phosphate containing both linie and sodium is formed on 

 heating such a mixture. 



Day's * process consists in heating (with or without a potash salt) 

 a natural or artificial mixture of phosphate rock, silica, and lime- 

 stone to a temperature just above that at which carbon dioxide is 

 driven off. He claims that the resulting product contains phosphoric 

 acid soluble in a 5 per cent solution of citric acid. The length of 

 time of heating required varies between rather wide limits, depend- 

 ing on the materials used and the thoroughness with which they 

 are mixed. w 



Rocour, 2 Newberry and Barrett, 3 Meriwether, 4 and Landis 5 have 

 devised processes in which double decomposition is brought about 

 by heating a mixture of phosphate rock and sodium sulphate, or 

 phosphate rock, lime, and sodium sulphate. Probably the process 

 under this head which has attracted the most attention is that of 

 Newberry and Barrett. It is understood that the process as worked 

 on a commercial scale differs somewhat from that described in the 

 original patent, but the general plan consists in submitting an inti- 

 mate mixture of phosphate rock and sodium sulphate to a constantly 

 increasing temperature till a temperature of about 2,800° F. is 

 reached. The clinker formed is then ground, sacked, and sold on 

 the basis of the citrate-soluble phosphoric acid which it contains. 

 It is also said that the final product contains a considerably higher 

 percentage of phosphoric acid than the original mixture, owing 

 to the volatilization of some of the products formed at the high 

 temperatures. 



While the reagents required (sodium chloride, sodium sulphate, 

 etc.) to convert phosphate rock into a citrate-soluble form in such 

 processes are comparatively cheap, the expense of maintaining the 

 necessary high temperatures for protracted periods adds considerably 

 to the cost of production. It is claimed, however, that in some of 

 these processes the cost of phosphoric acid per unit is less than it is 

 in acid phosphate. 



In order to utilize low-grade phosphates unfit for acid treatment, 

 Wiborgh, 8 Connor, 7 Newberry, 8 and Gait have devised processes in 

 whir-.li ground phosphate is mixed with an alkali hydroxide or car- 



1 United States Patent No. 542080 (1895). « United States Patent No. 001089 (1898). 



i United Statet Patent No. 284074 (1883). 7 United States Patents Nos. 931K40 (1909). 



• United Statet Patent No. 1042688(1012). 1042400, 1042401 (1012). 



• United Statet Patent No. 1068240(1013). e United States Patent No. 978193 (1910). 

 » UnH : (tent No. 1094867 (1014). ' United States Patent No. 1010989 (1912) 



