THE TERNARY SYSTEMS, POTASSIUM-PHOSPHORIC ACID-WATER AND AMMONIAPHOSPHORIC ACID-WATER BY E. G. P A R K E R ~
A question of considerable importance in fertilizer chemistry today is whether or no a concentrated fertilizer, that is, a fertilizer containing a high percent of the so-called plant foods, can be economically produced and used. A concentrated fertilizer can obviously be made by mixing in the desired proportions the various ingredients, which process would require the production of each ingredient separately and a final mixing. The object of this work was to ascertain whether stable chemical compounds containing the three most important of fertilizer constituents, potash, phosphoric acid, and ammonia, exist at ordinary temperatures. Although the subject has a t present been anything but exhaustively investigated, and further work is a t present being carried on with the hope of either a positive or a negative final conclusion, many valuable observations were made which makes desirable the publication of the present report of progress. The work was carried on in conjunction with other fertilizer investigations in this laboratory under the direction of Dr. Frank K. Cameron. The two three-component systems, namely, K20-PzObH20 .and NH3-P2Ob-H20, were first investigated, and isotherms obtained for each system. The temperature chosen was 25' Centigrade, and was kept constant in a thermostat to an accuracy of one-tenth of one degree throughout the experiment. These systems have already been explored, in part, by D'Ans and Schreiner.2 Potassium-Phosphoric Acid-Water Bottles containing various amounts of orthophosphoric acid and potassium hydroxide in solution and in contact ~
I
- .-
Scientist, Soil Laboratory Investigations Bureau of Soils. J. D'Ans and 0 Schreiner: Zeit. phys. Chem., 75, 95 (1910).
E. G. Parker
65 4
with a solid phase were placed in a thermostat and allowed to rotate until equilibrium was established. Portions of the liquid and solid phases at equilibrium were removed and examined. _____
-
_-~ _ -
Liquid phase
~~
_________~
~ _ _ _ _ _ _ _ _ _
Solid phase
1
Percent K I Po4 Percent K 1 Po4 I ______ I Mols per Mols per I 1000 gr. 1000gr. of solutioii,of solutio
1
Formula
Optical property
,
I I
-___
.40 1.47 2.31 1.89 1.78 I ,51 I .4h 2.31 2.61 3.06 3.20 3.98 5.22 5.33 5.67 I
6.80 7.23 7.79 8.56 8.81 7.14 7.18 9.19 9.23 9.41 9.79 9.80 9.48 9.76 9.76 9.77
1
8.56 6.74 5 .oo 3.20 2.60 1.81 I .46 I .84 1.99 2.25 2.28 2.67 3.24 3.33 3.41 3.69 3.92 3.73 3.66 3.42 2.92 2.07 2 .og 0.48 0.46 0.38 0.23
0.24 0.32 0.24 0.22 0. I 2
16.13 82.00 16.75 , 80.55 25.62 167.23 28.05 1 69.18 28.20 -
27.90 27.80
-
28.00 28.40 28.40 28. I O
-
28.30 28.80 28.50
-
-
-
-
13 .90 $3.60 -
13.85
-
42.60 $2.60 -
Uniaxial(-)
1 Uniaxial(-) I
Uniaxial (-1 Uniaxial(-) Uniaxial(-j Uniaxial(-) Uniaxial(-) Uniaxial (-) Uniaxial(-) Uniaxial (-) Uniaxial(-) Uniaxial(-) Uniaxial (-) Uniaxial (-) Uniaxial(-) Biaxial(+) Biaxial( +) Biaxial( +) Biaxial(-) Biaxial(-) Biaxial(-) Biaxial(-) Biaxial (-) Biaxial(-) Biaxial(-) Biaxial (-) -
-
’
The Ternary Systems, Etc.
655
Phosphoric acid was determined according to the method of B. Schmitz.l Potassium was determined by precipitation as potassium chlorplatinate. Some of the solid phases were primarily examined by chemical analysis, but on collecting sufficient data on their optical properties, some were identified microscopically by Mr. William H. Fry of this Bureau. The results of the examination of the various liquid and solid phases are given in the preceding table. From these results isotherms were plotted with mols of K per roo6 grams of solution as ordinates and mols of POe per 1000 grams of solution as abscissae (see Fig. I ) .
Fig. I-Concentration
isotherms for the three-component system K~O--P~O~-HZO at 2 5 O C
From Table I and Fig. I it appears that the stable solid phases in contact with solutions containing potassium and orthophosphoric acid at 2 5 O C are, KHZPO~.H~PO~ KH2P04 K3P01.3H20 KOH.2H20 1 ’
(1913).
Page 434 of Treadwell and Hall’s “Analytical Chemistry,” Vol. 11
E. G. Par&
656
The branch of the curve representing KH2P04 has, at a concentration of about 1.46 mols of K and 1.46 mols of PO4 per 1000 grams of solution, an apparent sharp break, and the addition of either potassium or phosphoric acid at this point increases the solubility of the monopotassium phosphate. It was thought possible that the monopotassium phosphate might exist in more than one modification, a transition taking place at about 25' C. Investigation by means of the dilatometric method showed this not to be the case (see Fig. 2 ) .
Fig. 2-Curve
showing the change in volume of KH2POd with increasing temperature
So that no doubt might exist that the solid phases stable on both sides of this apparent sharp point were chemically the same, they were all analyzed and plotted on a triangular diagram. The composition of the solid phases always corresponds to the formula KH2P04. (Point S-see Fig. 3.) The existence of an actual break or an intersection in the curve' would be a contradiction of the phase rule. The probability is that instead of a sharp break in the solubility curve for the phosphate with the formula KH2P04, it goes through an undetectable minimum a t this point as suggested by J. D'Ans and 0. Schreiner.l The significance of the fact that the ratio of potassium to phosphoric acid is I : I a t this minimum is not apparent. J . D'Ans axid 0. Schreiner, Zeit. yhys. Chem., 75, 95 (1910).
The Ternary Systcnzs, Etc.
b'ig. 3-Graphical
6s 7
representation for the determination of the composition of a solid phase
Ammonia-Phosphoric Acid-Water Bottles containing various amounts of ammonia and orthophosphoric acid in solution and in contact with a solid phase, were allowed to rotate in a thermostat until equilibrium was established. Portions of the solid and liquid phases at equilibrium were removed and examined. Ammonia was determined according to a standard method.' Some of the solid phases were identified by means of the microscope. The results of the examination of the various liquid and solid phases are given in Table 11. From these results isotherms were plotted with mols of NH4 per 1000 grams of solution as ordinate and mols of PO1 per 1000 grams of solution as abscissae (see Pig. 4). From Fig. 4 and Table I1 it appears that the stable solid phases in contact with solutions containing ammonia and orthophosphoric acid a t 2.5' C are (NJ&)H&'04 (NH&HP04 INH4)sP04.3H20 On the branch of the curve representing (NH,)H,POJ 1
Page 5g of Treadwell and Hall's "Analytical Chemistry," Vol. I1 (1913).
658
E. G. Parker
we find that the same sharp break is present as in the case of the KH2P04. The break in this case is not quite as sharp, indicating that the explanation offered for the case of the monopotassium phosphate to be correct. Along the curve for (NH4)3P04.3H20 from the point C to the left ammonia is given off from the liquid, hence the curve as it stands in
Fig. 4-Concentration
isotherms for the three-component system NHn--P20s--HzO a t 25' C
the figure is not theoretically correct, as pressure was considered constant throughout the experiment. It may, however, be assumed to be practically so. These two isotherms may now be considered to be in planes a t right angles to each other, and from these an isotherm for the four component system K40-NH3-P205-H2Q may be continued and be represented in space.
The Ternary Systems, Etc.
65 9
TABLE II-COMPOS~TION OF SOLID A N D LIQ~JID PHASES ~ - -
-
~
~-
~
_
Liquid phase ~
I
NH4 -~
Mols per
PO4 ~~
1 Mols per
1000
solution
_
_
_
~
I- _ _ _ ~ I
1
_
~
~
.
~ _-_____ _
~ ~
-
Solid phase
Formula
Optical property
~-
1000
solution -
2.40 2.45 2.58 2.58 4.04 5.23 7.21 7.30 7 .OI 6.90 6.27 4.28 4 . I9 6.59 8.75 11.48 14.08
3.62 2.64 2.57 2.67 3.30 3.77 4.75 4.764.38 3.95 3.412.57 I .83 1.33 0.87 0.43 0.41
'
Uniaxial (-) Uniaxial(-) Uniaxial(-) Uniaxial(-) Uniaxial(-) Uniaxial (-) Uniaxial(-) Uniaxial (-) Uniaxial(-) Uniaxial(-) Biaxial (6
