THE MANUFACTURE OF ACID PHOSPHATE. 5 



Table II. — Specific gravities and their equivalents in Baume degrees of sulphuric acid of 



various strengths. 



°B. 



Sp.gr. 



Per cent 

 H 2 S0 4 . 



°B. 



Sp. gr. 



Per cent 

 H 2 S0 4 . 



°B. 



Sp.gr. 



Per cent 

 H 2 SO/. 







1. 0000 



0.00 



25 



1.2083 



28.28 



49 



1.5104 



60.75 



1 



1. 0069 



1.02 



26 



1.2185 



29.53 



50 



1. 5263 



62.18 



2 



1.0140 



2.08 



27 



1. 2288 



30.79 



51 



1. 5426 



63.66 



3 



1.0211 



3.13 



28 



1.2393 



32. 05 



52 



1. 5591 



65.13 



4 



1.0284 



4.21 



29 



1. 2500 



33.33 



53 



1.5761 



66.63 



5 



1. 0357 



5.28 



30 



1. 2609 



34.63 



54 



1. 5934 



68.13 



6 



1. 0432 



6.37 



31 



1.2719 



35.93 



55 



1.6111 



69.65 



7 



1. 0507 



7.45 



32 



1. 2832 



37.26 



56 



1. 6292 



71.17 



8 



1. 0584 



8.55 



33 



1. 2946 



38.58 



57 



1.6477 



72.75 



9 



1. 0662 



9.66 



34 



1. 3063 



39.92 



58 



1. 6667 



74.36 



10 



1.0741 



10.77 



35 



1. 3182 



41.27 



59 



1. 6860 



75.99 



11 



1.0821 



11.89 



36 



1.3303 



42.63 



60 



1. 7059 



77.67 



12 



1. 0902 



13.01 



37 



1. 3426 



43.99 



61 



1. 7262 



79.43 



13 



1. 0985 



14.13 



38 



1.3551 



45.35 



62 



1. 7470 



81.30 



14 



1. 1069 



15.25 



39 



1. 3679 



46.72 



63 



1. 7683 



83.34 



15 



1. 1154 



16.38 



40 



1.3810 



48.10 



64 



1. 7901 



85.66 



16 



1.1240 



17.53 



41 



1. 3942 



49.47 



64^ 



1. 7957 



86.33 



17 



1. 1328 



18.71 



42 



1. 4078 



50.87 



64| 



1.8012 



87.04 



18 



1.1417 



19.89 



43 



1.4216 



52.26 



64| 



1. 8068 



87.81 



19 



1. 1508 



21.07 



44 



1. 4356 



53.66 



65 



1.8125 



88.65 



20 



1. 1600 



22.25 



45 



1.4500 



55.07 



65i 



1.8182 



89.55 



21 



1.1694 



23.43 



46 



1.4646 



56.48 



65J 



1. 8239 



90.60 



22 



1. 1789 



24.61 



47 



1. 4796 



57.90 



65* 



1. 8297 



91.80 



23 



1. 1885 



25.81 



48 



1. 4948 



59.32 



66 



1.8354 



93.19 



24 



1. 1983 



27.03 















THEORETICAL BASIS FOR THE MANUFACTURE OF ACID PHOSPHATES. 



The process of making acid phosphate was devised in order to 

 change the phosphoric acid contained in the substances just enumer- 

 ated into a more soluble or " available" condition. 



The phosphates of lime, as found in nature are highly basic com- 

 pounds or solid solutions offering considerable resistance to the sol- 

 vent influence of percolating meteoric or soil waters. The less basic 

 phosphates (those containing less lime, iron, alumina, or magnesia) 

 are more soluble in water. 1 Therefore, in order to bring about the 

 desiied change, an acid stronger than phosphoric acid is added in 

 sufficient quantity to combine with a portion of the lime, producing 

 a phosphate less basic and, consequently, more soluble. The reagent 

 which has been found best suited for this purpose is sulphuric acid, 

 not only because of its cheapness but because calcium sulphate, one 

 of the products of the reaction, takes up the excess of water present 

 in the acid phosphate to form gypsum. The final product, there- 

 fore, if properly made, is dry and can be readily mixed with other 

 ingredients to make a complete fertilizer. 



The main purpose sought to be accomplished in the factory treat- 

 ment of phosphate rock is to prepare a product in which the phos- 

 phoric acid will be water soluble, so far as this can be accomplished, 

 with due regard to the physical properties of the product essential 

 to its ready mixing and handling. While it is a matter of no great 

 difficulty to determine by a chemical analysis just what constitu- 

 ents are in a given phosphate rock and in what proportions, it is not 



1 Bui. 41, Bureau of Soils, U. S Dept. Agr. (1907). 



