IUPAC-NIST Solubilities Database

IUPAC-NIST Solubility Database
NIST Standard Reference Database 106

Solubility System: Ammonium dihydrogenphosphate with Diammonium hydrogenphosphate, Urea and Water

Components:
   (1) Ammonium dihydrogenphosphate; NH4H2PO4; [7722-76-1]  NIST Chemistry WebBook for detail
   (2) Diammonium hydrogenphosphate; (NH4)2HPO4; [7783-28-0]  NIST Chemistry WebBook for detail
   (3) Urea; CH4N2O; [57-13-6]  NIST Chemistry WebBook for detail
   (4) Water; H2O; [7732-18-5]  NIST Chemistry WebBook for detail

Original Measurements:
   Ivanov, D.G.; Grantscharov, I.N., God. Vissh. Khimikotekhnol. Inst. Sofiya 1966, 13, 165.

Variables:

   Concentration = Temperature and composition in solutions with a NH₃/H₃PO₄ ratio = 1.8.

Prepared By:
   J. Eysseltová

Experimental Remarks:

   Remarks: Part 3. COMMENTS AND ADDITIONAL DATA: The authors presented the following equations relating total plant food to temperature and to the P₂O₅/N ratio. N + P₂O₅ = a + b(T-273.16) P₂O₅/N is constant[1] the equilibrium solid phase is constant

N + P₂O₅ = c + d(P₂O₅/N) T is constant[2] N + P₂O₅ = e + f(P₂O₅/N) + g(T-273.16)(P₂O₅/N)h[3] The values of the constants are summarized in the Table below. COMMENT: The equations describe the experimental data with a relative error of ±0.5%.

Experimental Data: (Notes on the Nomenclature)
(Please see footnotes following the table(s).)

Part 1. Solubility values in the CO(NH₂)₂-NH₄H₂PO₄-(NH₄)₂HPO₄-(H₂O) system un solutions having a mol ratio NH₃/H₃PO₄ = 1.8.
Solution number	T/K^(b)	Chemical₁	10² * Mass Fraction w₁	Chemical₂	10² * Mass Fraction w₂	Chemical₃	10² * Mass Fraction w₃	Chemical₄	10² * Mass Fraction w₄	Chemical₅	10² * Mass Fraction w₅	Chemical₆	10² * Mass Fraction w₆	Solid Phase(s)
1	339.5	N(NH3)	2.47	N(ur)	23.51	N(tot)	25.98	P2O5	6.95	N+P2O5	32.93	N:P2O5	1:0.27	(NH4)2HPO4
2	313.5	N(NH3)	1.23	N(ur)	26.45	N(tot)	27.68	P2O5	3.47	N+P2O5	31.15	N:P2O5	1:0.13	urea
3	314.1	N(NH3)	---	N(ur)	29.40	N(tot)	29.40	P2O5	---	N+P2O5	29.40	N:P2O5	1:0.00	"
4	328.4	N(NH3)	2.39	N(ur)	22.77	N(tot)	25.16	P2O5	6.73	N+P2O5	31.98	N:P2O5	1:0.27	(NH4)2HPO4
5	309.6	N(NH3)	1.20	N(ur)	25.61	N(tot)	26.81	P2O5	3.37	N+P2O5	30.18	N:P2O5	1:0.13	urea
6	310.8	N(NH3)	---	N(ur)	28.50	N(tot)	28.50	P2O5	---	N+P2O5	28.50	N:P2O5	1:0.00	"
7	338.1	N(NH3)	3.47	N(ur)	19.26	N(tot)	22.73	P2O5	9.86	N+P2O5	32.59	N:P2O5	1:0.43	(NH4)2HPO4
8	303.1	N(NH3)	2.31	N(ur)	22.02	N(tot)	22.33	P2O5	6.51	N+P2O5	30.84	N:P2O5	1:0.27	urea
9	305.0	N(NH3)	1.15	N(ur)	24.77	N(tot)	25.92	P2O5	3.25	N+P2O5	29.17	N:P2O5	1:0.13	"
10	306.7	N(NH3)	---	N(ur)	27.50	N(tot)	27.50	P2O5	---	N+P2O5	27.50	N:P2O5	1:0.00	"
11	338.8	N(NH3)	4.47	N(ur)	15.96	N(tot)	20.43	P2O5	12.58	N+P2O5	33.01	N:P2O5	1:0.62	(NH4)2HPO4
12	325.1	N(NH3)	3.35	N(ur)	18.62	N(tot)	21.97	P2O5	9.44	N+P2O5	31.41	N:P2O5	1:0.43	"
13	298.6	N(NH3)	2.23	N(ur)	21.28	N(tot)	23.51	P2O5	6.29	N+P2O5	29.80	N:P2O5	1:0.27	urea
14	301.6	N(NH3)	1.12	N(ur)	23.93	N(tot)	25.05	P2O5	3.15	N+P2O5	28.20	N:P2O5	1:0.13	"
15	302.8	N(NH3)	---	N(ur)	26.60	N(tot)	26.60	P2O5	---	N+P2O5	26.60	N:P2O5	1:0.00	"
16	338.8	N(NH3)	10.78	N(ur)	---	N(tot)	10.78	P2O5	30.35	N+P2O5	41.13	N:P2O5	1:2.82	(NH4)2HPO4
17	337.7	N(NH3)	9.70	N(ur)	2.57	N(tot)	12.27	P2O5	27.31	N+P2O5	39.58	N:P2O5	1:2.23	"
18	337.6	N(NH3)	8.62	N(ur)	5.13	N(tot)	13.75	P2O5	24.28	N+P2O5	38.03	N:P2O5	1:1.77	"
19	337.0	N(NH3)	7.54	N(ur)	7.70	N(tot)	15.24	P2O5	21.24	N+P2O5	36.48	N:P2O5	1:1.39	(NH4)2HPO4
20	335.4	N(NH3)	6.47	N(ur)	10.26	N(tot)	16.73	P2O5	18.21	N+P2O5	34.94	N:P2O5	1:1.09	"
21	331.4	N(NH3)	5.39	N(ur)	12.83	N(tot)	18.22	P2O5	15.17	N+P2O5	33.39	N:P2O5	1:0.83	"
22	321.9	N(NH3)	4.31	N(ur)	15.40	N(tot)	19.71	P2O5	12.13	N+P2O5	31.84	N:P2O5	1:0.62	"
23	308.0	N(NH3)	3.23	N(ur)	17.96	N(tot)	21.19	P2O5	9.10	N+P2O5	30.29	N:P2O5	1:0.43	"
24	293.8	N(NH3)	2.15	N(ur)	20.53	N(tot)	22.68	P2O5	6.07	N+P2O5	28.75	N:P2O5	1:0.27	urea
25	296.4	N(NH3)	1.08	N(ur)	23.09	N(tot)	24.17	P2O5	3.03	N+P2O5	27.30	N:P2O5	1:0.13	"
26	298.8	N(NH3)	---	N(ur)	25.60	N(tot)	25.60	P2O5	---	N+P2O5	25.60	N:P2O5	1:0.00	"
27	325.0	N(NH3)	10.19	N(ur)	---	N(tot)	10.19	P2O5	28.69	N+P2O5	38.88	N:P2O5	1:2.82	(NH4)2HPO4
28	323.9	N(NH3)	9.17	N(ur)	2.43	N(tot)	11.60	P2O5	25.82	N+P2O5	37.42	N:P2O5	1:2.23	"
29	322.8	N(NH3)	8.15	N(ur)	4.85	N(tot)	13.00	P2O5	22.95	N+P2O5	35.95	N:P2O5	1:1.77	"
30	321.5	N(NH3)	7.13	N(ur)	7.28	N(tot)	14.41	P2O5	20.08	N+P2O5	34.49	N:P2O5	1:1.39	"
31	318.2	N(NH3)	6.11	N(ur)	9.70	N(tot)	15.81	P2O5	17.21	N+P2O5	33.02	N:P2O5	1:1.09	"
32	312.8	N(NH3)	5.09	N(ur)	12.13	N(tot)	17.22	P2O5	14.34	N+P2O5	31.56	N:P2O5	1:0.83	"
33	303.7	N(NH3)	4.08	N(ur)	14.55	N(tot)	18.63	P2O5	11.47	N+P2O5	30.10	N:P2O5	1:0.62	"
34	286.7	N(NH3)	3.06	N(ur)	16.98	N(tot)	20.04	P2O5	8.61	N+P2O5	28.65	N:P2O5	1:0.43	"
35	289.2	N(NH3)	2.04	N(ur)	19.41	N(tot)	21.45	P2O5	5.74	N+P2O5	27.19	N:P2O5	1:0.27	urea
36	292.2	N(NH3)	1.02	N(ur)	21.83	N(tot)	22.85	P2O5	2.87	N+P2O5	25.72	N:P2O5	1:0.13	"
37	293.3	N(NH3)	---	N(ur)	24.30	N(tot)	24.30	P2O5	---	N+P2O5	24.30	N:P2O5	1:0.00	"
38	315.8	N(NH3)	9.80	N(ur)	---	N(tot)	9.80	P2O5	27.58	N+P2O5	37.38	N:P2O5	1:2.82	(NH4)2HPO4
39	314.5	N(NH3)	8.82	N(ur)	2.33	N(tot)	11.15	P2O5	24.83	N+P2O5	35.98	N:P2O5	1:2.23	"
40	312.9	N(NH3)	7.84	N(ur)	4.66	N(tot)	12.50	P2O5	22.07	N+P2O5	34.57	N:P2O5	1:1.77	"
41	311.3	N(NH3)	6.86	N(ur)	7.00	N(tot)	13.66	P2O5	19.31	N+P2O5	33.17	N:P2O5	1:1.39	"
42	307.5	N(NH3)	5.88	N(ur)	9.33	N(tot)	15.21	P2O5	16.55	N+P2O5	31.76	N:P2O5	1:1.09	"
43	300.8	N(NH3)	4.90	N(ur)	11.66	N(tot)	16.56	P2O5	13.79	N+P2O5	30.35	N:P2O5	1:0.83	"
44	290.2	N(NH3)	3.92	N(ur)	13.99	N(tot)	17.91	P2O5	11.03	N+P2O5	28.94	N:P2O5	1:0.62	"
45	283.2	N(NH3)	2.94	N(ur)	16.33	N(tot)	19.27	P2O5	8.27	N+P2O5	27.54	N:P2O5	1:0.43	urea
46	285.7	N(NH3)	1.96	N(ur)	18.66	N(tot)	20.62	P2O5	5.52	N+P2O5	26.14	N:P2O5	1:0.27	"
47	288.5	N(NH3)	0.98	N(ur)	20.99	N(tot)	21.97	P2O5	2.76	N+P2O5	24.73	N:P2O5	1:0.13	"
48	289.8	N(NH3)	---	N(ur)	23.30	N(tot)	23.30	P2O5	---	N+P2O5	23.30	N:P2O5	1:0.00	"
49	305.4	N(NH3)	9.41	N(ur)	---	N(tot)	9.41	P2O5	26.48	N+P2O5	35.89	N:P2O5	1:2.82	(NH4)2HPO4
50	304.4	N(NH3)	8.47	N(ur)	2.24	N(tot)	10.71	P2O5	23.84	N+P2O5	34.55	N:P2O5	1:2.23	"
51	303.1	N(NH3)	7.52	N(ur)	4.48	N(tot)	12.00	P2O5	21.19	N+P2O5	33.19	N:P2O5	1:1.77	"
52	299.4	N(NH3)	6.58	N(ur)	6.72	N(tot)	13.30	P2O5	18.54	N+P2O5	31.84	N:P2O5	1:1.39	"
53	294.8	N(NH3)	5.64	N(ur)	8.96	N(tot)	14.60	P2O5	15.89	N+P2O5	30.49	N:P2O5	1:1.09	"
54	289.5	N(NH3)	4.70	N(ur)	11.20	N(tot)	15.90	P2O5	13.24	N+P2O5	29.14	N:P2O5	1:0.83	"
55	275.7	N(NH3)	3.76	N(ur)	13.44	N(tot)	17.20	P2O5	10.59	N+P2O5	27.79	N:P2O5	1:0.62	"
56	279.2	N(NH3)	2.82	N(ur)	15.68	N(tot)	18.50	P2O5	7.95	N+P2O5	26.45	N:P2O5	1:0.43	urea
57	282.0	N(NH3)	1.88	N(ur)	17.92	N(tot)	19.80	P2O5	5.30	N+P2O5	25.10	N:P2O5	1:0.27	"
58	283.3	N(NH3)	0.94	N(ur)	20.15	N(tot)	21.09	P2O5	2.65	N+P2O5	23.74	N:P2O5	1:0.13	"
59	296.1	N(NH3)	---	N(ur)	22.40	N(tot)	22.40	P2O5	---	N+P2O5	22.40	N:P2O5	1:0.00	"
60	291.1	N(NH3)	8.83	N(ur)	---	N(tot)	8.83	P2O5	24.85	N+P2O5	33.68	N:P2O5	1:2.82	(NH4)2HPO4
61	287.0	N(NH3)	7.94	N(ur)	2.10	N(tot)	10.04	P2O5	22.37	N+P2O5	32.41	N:P2O5	1:2.23	"
62	287.0	N(NH3)	7.06	N(ur)	4.20	N(tot)	11.26	P2O5	19.88	N+P2O5	31.14	N:P2O5	1:1.77	"
63	284.0	N(NH3)	6.18	N(ur)	6.30	N(tot)	12.48	P2O5	17.40	N+P2O5	29.88	N:P2O5	1:1.39	"
64	278.9	N(NH3)	5.30	N(ur)	8.40	N(tot)	13.70	P2O5	14.91	N+P2O5	28.61	N:P2O5	1:1.09	"
65	271.7	N(NH3)	4.41	N(ur)	10.51	N(tot)	14.92	P2O5	12.42	N+P2O5	27.34	N:P2O5	1:0.83	"
66	270.8	N(NH3)	3.53	N(ur)	12.61	N(tot)	16.14	P2O5	9.94	N+P2O5	26.08	N:P2O5	1:0.62	urea
67	273.8	N(NH3)	2.65	N(ur)	14.71	N(tot)	17.36	P2O5	7.45	N+P2O5	24.81	N:P2O5	1:0.43	"
68	277.1	N(NH3)	1.76	N(ur)	16.81	N(tot)	18.57	P2O5	4.76	N+P2O5	23.54	N:P2O5	1:0.27	"
69	280.2	N(NH3)	0.88	N(ur)	18.91	N(tot)	19.79	P2O5	2.48	N+P2O5	22.27	N:P2O5	1:0.13	"
70	281.5	N(NH3)	---	N(ur)	21.00	N(tot)	21.00	P2O5	---	N+P2O5	21.00	N:P2O5	1:0.00	"
71	282.5	N(NH3)	8.43	N(ur)	---	N(tot)	8.43	P2O5	23.73	N+P2O5	32.16	N:P2O5	1:2.82	(NH4)2HPO4
72	281.7	N(NH3)	7.58	N(ur)	2.01	N(tot)	9.59	P2O5	21.35	N+P2O5	30.94	N:P2O5	1:2.23	(NH4)2HPO4
73	278.0	N(NH3)	6.74	N(ur)	4.01	N(tot)	10.75	P2O5	18.93	N+P2O5	29.73	N:P2O5	1:1.77	"
74	274.1	N(NH3)	5.90	N(ur)	6.52	N(tot)	11.92	P2O5	16.61	N+P2O5	28.53	N:P2O5	1:1.39	"
75	272.8	N(NH3)	1.69	N(ur)	16.05	N(tot)	17.74	P2O5	4.75	N+P2O5	22.49	N:P2O5	1:0.27	urea
76	274.8	N(NH3)	0.84	N(ur)	18.06	N(tot)	18.90	P2O5	2.37	N+P2O5	21.27	N:P2O5	1:0.13	"

Part 2. The compiler has recalculated the data in Part 1 to give the following concentration values.
Solution number	Chemical₁	10² * Mass Fraction w₁	m₁ [mol/kg]	Chemical₂	10² * Mass Fraction w₂	m₂ [mol/kg]	Chemical₃	10² * Mass Fraction w₃	m₃ [mol/kg]	Chemical₄	10² * Mass Fraction w₄
1	CO(NH2)2	50.43	22.71	(NH4)2HPO4	10.33	2.11	NH4H2PO4	2.27	0.53	H2O	36.98
2	CO(NH2)2	56.74	25.54	(NH4)2HPO4	5.13	1.05	NH4H2PO4	1.16	0.27	H2O	36.98
3	CO(NH2)2	63.06	28.43	(NH4)2HPO4	0.00	0.00	NH4H2PO4	0.00	0.00	H2O	36.94
4	CO(NH2)2	48.84	20.87	(NH4)2HPO4	9.98	1.94	NH4H2PO4	2.21	0.49	H2O	38.97
5	CO(NH2)2	54.93	23.48	(NH4)2HPO4	5.03	0.98	NH4H2PO4	1.08	0.24	H2O	38.96
6	CO(NH2)2	61.13	26.19	(NH4)2HPO4	0.00	0.00	NH4H2PO4	0.00	0.00	H2O	38.87
7	CO(NH2)2	41.31	16.83	(NH4)2HPO4	14.33	2.66	NH4H2PO4	3.50	0.74	H2O	40.86
8	CO(NH2)2	47.23	19.19	(NH4)2HPO4	9.64	1.78	NH4H2PO4	2.15	0.46	H2O	40.97
9	CO(NH2)2	53.13	21.58	(NH4)2HPO4	4.78	0.88	NH4H2PO4	1.10	0.23	H2O	40.99
10	CO(NH2)2	58.99	23.95	(NH4)2HPO4	0.00	0.00	NH4H2PO4	0.00	0.00	H2O	41.01
11	CO(NH2)2	34.23	13.26	(NH4)2HPO4	18.68	3.29	NH4H2PO4	4.11	0.83	H2O	42.97
12	CO(NH2)2	39.94	15.48	(NH4)2HPO4	13.98	2.46	NH4H2PO4	3.12	0.63	H2O	42.96
13	CO(NH2)2	45.65	17.69	(NH4)2HPO4	9.30	1.64	NH4H2PO4	2.10	0.42	H2O	42.96
14	CO(NH2)2	51.33	19.89	(NH4)2HPO4	4.69	0.83	NH4H2PO4	1.02	0.21	H2O	42.96
15	CO(NH2)2	57.06	22.12	(NH4)2HPO4	0.00	0.00	NH4H2PO4	0.00	0.00	H2O	42.94
16	CO(NH2)2	0.00	0.00	(NH4)2HPO4	45.04	7.58	NH4H2PO4	9.95	1.92	H2O	45.01
17	CO(NH2)2	5.51	2.04	(NH4)2HPO4	40.53	6.82	NH4H2PO4	8.95	1.73	H2O	45.01
18	CO(NH2)2	11.00	4.07	(NH4)2HPO4	35.99	6.06	NH4H2PO4	7.99	1.54	H2O	45.01
19	CO(NH2)2	16.52	6.11	(NH4)2HPO4	31.48	5.30	NH4H2PO4	7.00	0.35	H2O	45.01
20	CO(NH2)2	22.01	8.14	(NH4)2HPO4	27.04	4.55	NH4H2PO4	5.95	1.15	H2O	45.00
21	CO(NH2)2	27.52	10.18	(NH4)2HPO4	22.53	3.79	NH4H2PO4	4.96	0.96	H2O	44.99
22	CO(NH2)2	33.03	12.23	(NH4)2HPO4	18.02	3.03	NH4H2PO4	3.96	0.77	H2O	44.99
23	CO(NH2)2	38.52	14.26	(NH4)2HPO4	13.48	2.27	NH4H2PO4	3.00	0.58	H2O	44.99
24	CO(NH2)2	44.04	16.30	(NH4)2HPO4	8.95	1.51	NH4H2PO4	2.04	0.39	H2O	44.97
25	CO(NH2)2	49.53	18.33	(NH4)2HPO4	4.53	0.76	NH4H2PO4	0.96	0.19	H2O	44.98
26	CO(NH2)2	54.91	20.28	(NH4)2HPO4	0.00	0.00	NH4H2PO4	0.00	0.00	H2O	45.09
27	CO(NH2)2	0.00	0.00	(NH4)2HPO4	42.57	6.71	NH4H2PO4	9.41	1.70	H2O	48.02
28	CO(NH2)2	5.21	1.81	(NH4)2HPO4	38.31	6.04	NH4H2PO4	8.47	1.53	H2O	48.01
29	CO(NH2)2	10.40	3.61	(NH4)2HPO4	34.04	5.37	NH4H2PO4	7.54	1.36	H2O	48.02
30	CO(NH2)2	15.62	5.41	(NH4)2HPO4	29.62	4.67	NH4H2PO4	6.74	1.22	H2O	48.03
31	CO(NH2)2	20.81	7.21	(NH4)2HPO4	25.51	4.02	NH4H2PO4	5.66	1.03	H2O	48.02
32	CO(NH2)2	26.02	9.02	(NH4)2HPO4	21.25	3.35	NH4H2PO4	4.73	0.86	H2O	48.00
33	CO(NH2)2	31.21	10.83	(NH4)2HPO4	17.08	2.69	NH4H2PO4	3.71	0.67	H2O	48.00
34	CO(NH2)2	36.42	12.64	(NH4)2HPO4	12.79	2.02	NH4H2PO4	2.81	0.51	H2O	47.98
35	CO(NH2)2	41.63	14.45	(NH4)2HPO4	8.53	1.35	NH4H2PO4	1.87	0.34	H2O	47.96
36	CO(NH2)2	46.83	16.25	(NH4)2HPO4	4.26	0.67	NH4H2PO4	0.94	0.17	H2O	47.97
37	CO(NH2)2	52.12	18.13	(NH4)2HPO4	0.00	0.00	NH4H2PO4	0.00	0.00	H2O	47.88
38	CO(NH2)2	0.00	0.00	(NH4)2HPO4	40.97	6.20	NH4H2PO4	9.01	1.57	H2O	50.03
39	CO(NH2)2	5.00	1.66	(NH4)2HPO4	36.85	5.58	NH4H2PO4	8.13	1.41	H2O	50.01
40	CO(NH2)2	10.00	3.33	(NH4)2HPO4	32.76	4.96	NH4H2PO4	7.23	1.26	H2O	50.02
41	CO(NH2)2	15.02	5.00	(NH4)2HPO4	28.67	4.34	NH4H2PO4	6.32	1.10	H2O	50.00
42	CO(NH2)2	20.01	6.66	(NH4)2HPO4	24.58	3.72	NH4H2PO4	5.41	0.94	H2O	50.00
43	CO(NH2)2	25.01	8.33	(NH4)2HPO4	20.48	3.10	NH4H2PO4	4.50	0.78	H2O	50.00
44	CO(NH2)2	30.01	9.99	(NH4)2HPO4	16.39	2.48	NH4H2PO4	3.60	0.63	H2O	50.00
45	CO(NH2)2	35.03	11.67	(NH4)2HPO4	12.30	1.86	NH4H2PO4	2.69	0.47	H2O	49.99
46	CO(NH2)2	40.03	13.34	(NH4)2HPO4	8.19	1.24	NH4H2PO4	1.81	0.32	H2O	49.97
47	CO(NH2)2	45.02	15.00	(NH4)2HPO4	4.09	0.62	NH4H2PO4	0.91	0.16	H2O	49.98
48	CO(NH2)2	49.98	16.64	(NH4)2HPO4	0.00	0.00	NH4H2PO4	0.00	0.00	H2O	50.02
49	CO(NH2)2	0.00	0.00	(NH4)2HPO4	39.34	5.73	NH4H2PO4	8.64	1.44	H2O	52.02
50	CO(NH2)2	4.80	1.54	(NH4)2HPO4	35.40	5.15	NH4H2PO4	7.80	1.30	H2O	52.00
51	CO(NH2)2	9.61	3.08	(NH4)2HPO4	31.39	4.57	NH4H2PO4	7.00	1.17	H2O	52.01
52	CO(NH2)2	14.41	4.62	(NH4)2HPO4	27.46	4.00	NH4H2PO4	6.12	1.02	H2O	52.00
53	CO(NH2)2	19.22	6.15	(NH4)2HPO4	23.54	3.43	NH4H2PO4	5.24	0.88	H2O	52.00
54	CO(NH2)2	24.02	7.69	(NH4)2HPO4	19.62	2.86	NH4H2PO4	4.36	0.73	H2O	51.99
55	CO(NH2)2	28.83	9.23	(NH4)2HPO4	15.70	2.29	NH4H2PO4	3.48	0.58	H2O	51.99
56	CO(NH2)2	33.63	10.78	(NH4)2HPO4	11.76	1.71	NH4H2PO4	2.64	0.44	H2O	51.97
57	CO(NH2)2	38.44	12.32	(NH4)2HPO4	7.84	1.14	NH4H2PO4	1.76	0.29	H2O	51.96
58	CO(NH2)2	43.22	13.85	(NH4)2HPO4	3.92	0.57	NH4H2PO4	0.88	0.15	H2O	51.98
59	CO(NH2)2	48.05	15.40	(NH4)2HPO4	0.00	0.00	NH4H2PO4	0.00	0.00	H2O	51.95
60	CO(NH2)2	0.00	0.00	(NH4)2HPO4	36.91	5.08	NH4H2PO4	8.12	1.28	H2O	54.97
61	CO(NH2)2	4.50	1.36	(NH4)2HPO4	33.14	4.57	NH4H2PO4	7.38	1.17	H2O	54.97
62	CO(NH2)2	9.01	2.73	(NH4)2HPO4	29.49	4.06	NH4H2PO4	6.53	1.03	H2O	54.97
63	CO(NH2)2	13.51	4.09	(NH4)2HPO4	25.82	3.56	NH4H2PO4	5.71	0.90	H2O	54.96
64	CO(NH2)2	18.02	5.46	(NH4)2HPO4	22.17	3.05	NH4H2PO4	4.85	0.77	H2O	54.96
65	CO(NH2)2	22.54	6.83	(NH4)2HPO4	18.42	2.54	NH4H2PO4	4.08	0.65	H2O	54.95
66	CO(NH2)2	27.05	8.20	(NH4)2HPO4	14.75	2.03	NH4H2PO4	3.26	0.52	H2O	54.94
67	CO(NH2)2	31.55	9.56	(NH4)2HPO4	11.09	1.53	NH4H2PO4	2.41	0.38	H2O	54.94
68	CO(NH2)2	36.06	10.87	(NH4)2HPO4	7.72	1.06	NH4H2PO4	0.99	0.16	H2O	55.23
69	CO(NH2)2	40.56	12.29	(NH4)2HPO4	3.67	0.51	NH4H2PO4	0.82	0.13	H2O	54.95
70	CO(NH2)2	45.05	13.65	(NH4)2HPO4	0.00	0.00	NH4H2PO4	0.00	0.00	H2O	54.96
71	CO(NH2)2	0.00	0.00	(NH4)2HPO4	35.23	4.68	NH4H2PO4	7.77	1.18	H2O	57.00
72	CO(NH2)2	4.31	1.26	(NH4)2HPO4	31.65	4.20	NH4H2PO4	7.03	1.07	H2O	57.01
73	CO(NH2)2	8.60	2.51	(NH4)2HPO4	28.15	3.74	NH4H2PO4	6.23	0.95	H2O	57.01
74	CO(NH2)2	13.99	4.16	(NH4)2HPO4	24.65	3.34	NH4H2PO4	5.44	0.85	H2O	55.92
75	CO(NH2)2	34.43	10.06	(NH4)2HPO4	7.08	0.94	NH4H2PO4	1.53	0.23	H2O	56.96
76	CO(NH2)2	38.74	11.32	(NH4)2HPO4	3.50	0.47	NH4H2PO4	0.79	0.12	H2O	56.97

Notes:
   Table 1  ^a  This is a number characterizing the respective section. It is close to, but not identical with the total salt content of the system.
   Table 1  ^b  This is the temperature of crystallization.

Method/Apparatus/Procedure:
   A visual polythermic method was used. The apparatus consisted of 2 thermostated reaction vessels, the contents of which were stirred vigorously. The appearance/disappearance of the last crystal was observed with a stereomicroscope. The composition of the equilibrium solid phases was determined analytically. Nitrogen (total and ammoniacal) was determined by the Kjeldahl method. Phosphate ions were precipitated as NH₄MgPO₄·6H₂O and the excess Mg was titrated complexometrically using eriochrome black T as indicator.

Source and Purity of Materials:
   Reagent grade urea, NH₄H₂PO₄ and (NH₄)₂HPO₄ were recrystallized before being used.

Estimated Errors:

   Temperature: The reproducibility of the crystallization temperature was within 0.3 K. For the correlations see EXPERIMENTAL VALUES.