PHOSPHATE ROCK: 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 lime 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. 
Rocour,? Newberry and Barrett,? Meriwether,‘ and Landis*® 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,® Connor,’ Newberry,® and Galt ® have devised processes in 
which ground phosphate is mixed with an alkali hydroxide or car- 
1 United States Patent No. 542080 (1895). 6 United States Patent No. 601089 (1898). 
2 United States Patent No. 284674 (1883). 7 United States Patents Nos. 931846 (1909). 
3 United States Patent No. 1042588 (1912). 1042400, 1042401 (1912). 
4 United States Patent No. 1058249 (1913). ® United States Patent No. 978193 (1910). 
5 United States Patent No. 1094857 (1914). 9 United States Patent No. 1016989 (1912) 
