114 CONTRIBUTIONS TO CHEMISTRY AND MINERALOGY. [bull.167 
Dried at 100° it gave: 
Calculated for 
P 2 N0 6 H 2 Ag 3 . 
Found. 
l. 
2. 
3. 
4. 
12.60 
2.96 
65.06 
5. 
p .... 
N.... 
Ag-~ 
12.47 
2.82 
65.03 
13.19 
3.13 
63.70 
12.75 
3.14 
63.87 
12.34 
2.86 
65.21 
12. 19 
2.92 
66.46 | 
1 
1. P : N : Ag = 2 : 1.05 : 2.78. 
2. P :N : Ag = 2 : 1.09 : 2.78. 
3. P : N : Ag = 2 : 1.02 : 3.04. 
4. P : N : Ag = 2 : 1.04 : 2.97. 
5. P : N : Ag = 2 : 1.06 : 3.14. 
Tetra-silver imido diphosphate, P 2 NO G HAg 1 . — This salt exists in ; 
white and in a yellow form. The former is obtained by precipitating ; 
solution of silver oxide in ammonium nitrate by the sodium salt. I 
forms a voluminous, flocculent precipitate, which remains white only ii 
presence of its mother liquor; on washing out it undergoes partia 
transformation into the yellow form, the same change occurring tern 
porarily on boiling under the mother liquor. It shows a slight dec 
ciency of silver (analysis 4). 
The yellow form is obtained as an amorphous, flocculent precipitat 
by adding an ammoniacal solution of an imidodiphosphate to an exces 
of silver nitrate (analyses 1-2), or as an imperfectly crystalline powder 
by evaporating such an ammoniacal solution, containing an excess o 
silver, over sulphuric acid (analysis 3). From this it appears that thi 
remaining hydrogen atom is not replaceable by metal. The differenc 
between the white and yellow forms is perhaps due to tautomerism. 
Dried at 100°, it gave : 
Calculated for 
P 2 N0 6 HAg 4 . 
Found. 
1. 
2. 3. 
4. 
p .. 
10.27 
2.32 
71.39 
10.17 
2.28 
72.19 
10. 07 
10.80 
N 
2.45 
Ag 
72. 35 71. 01 
69. 72 
1. P : N : Ag = 2 : 0.99 : 4.01. 
2. P : N : Ag = 2 : 1.07 : 4.13. 
3. P : Ag = 2 : 3.71. 
Imidodiphosphoric acid is easily distinguished from diimidotriphos 
phoric acid by the insolubility of its magnesium salt, by the peculia 
granular or lumpy appearance of its tertiary silver salt, by its sirup; 
