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 
HoSO*. 
°B. 
Sp. gr. 
Tor cent 
B2SO4. 
°B. 
Sp. gr. 
For cvnt 
I!, SO, 

1.0000 
0.00 
25 
1.2083 
28.28 
49 
1.5104 
60.-75 
1 
L.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 
82. 05 
52 
1.5591 
65. 13 
4 
L.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 
1.09S5 
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 
64i 
1. 7957 
86.33 
17 
1. 1328 
18.71 
42 
1. 4078 
50.87 
644- 
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 
65J 
1. 8182 
89.55 
21 
1. 1694 
23.43 
46 
1.4646 
56.48 
65.| 
1. 8239 
90.60 
22 
1. 1789 
24.61 
47 
1.4796 
57.90 
653- 
1. 8297 
91.80 
23 
1. 1885 
25. 81 
48 
1. 4948 
59.32 
66 
1. 8354 
93.19 
24 
1 
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 
deshed 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). 
