110 
CONTRIBUTIONS TO CHEMISTRY AND MINERALOGY. 
[bull. ig"( 
remains in solution. To get rid of it entirely, as well as of traces o 
orthophosphoric acid and of a substance of relatively high percentage 
of nitrogen, the tri-silver imidodiphosphate must be dissolved in am 
monia, reprecipitated as magnesium salt, pressed out, and reconvertec 
into the silver salt in the same manner. The mother liquor of tin 
second silver precipitation, if neutralized with ammonia, gives a mix 
ture of silver imidodiphosphate and pyrophosx^hate. This, after conver- 
sion into the sodium salt by sodium chloride, addition of a little caustic 
soda, and precipitating by alcohol, gives a sirup which is converted bj 
vigorous rubbing into a pasty mass. This, by repeated solution ant 
reprecipitation by alcohol, gives the characteristic fiat prisms of sodiun 
pyrophosphate. After conversion into the silver salt this proved to be 
free from nitrogen and an analysis gave: 
Ag 
Calculated for 
Ag 4 P 2 7 . 
Found. 
71.27 
70.23 
Tedious as the above method is, many experiments have failed to lead 
to the discovery of a better one, and have convinced me that it cannot 
be abbreviated in the least without injuriously affecting the quality ol 
the products. 
DlIMIDOTEIPHOSPHORIC Aril), r.N.,() 8 H 7 . 
This acid forms two series of salts in which 8 and 5 atoms of hydro- 
gen are replaced. The alkali salts with 3 atoms of metal are of neutral ; 
those with 5 atoms of alkaline reaction. It seems impossible to replace 
the 2 remaining atoms, as is pointed out under the silver salts. 
- Tri- sodium diimidotriphosphate, P 3 N20 8 H 4 Na3. — The preparation of 
this salt is described above. It is easily soluble in water, this solution 
leaving on evaporation a mass of indistinct prisms. Precipitated from 
its aqueous solution by alcohol, it usually forms granules without evi- 
dence of crystalline form; but when very slowly precipitated it may be 
obtained as flat, very obtusely pointed prisms or rhombic plates, visible 
only when magnified 400 diameters. It contains no crystal water. The 
substance dried at 100° gave: 
Calculated for -cv^./i 
P 3 N 2 8 H 4 Na 3 . Fo,m(L 
p 
28. 89 28. 73 
8. 72 8. 77 
21.45 20.69 
i 
N 
Na 
P : N : Na. 
2.02 : 2.92. 
A penta-sodium salt probably exists, being obtained by decomposing 
the penta-silver salt with sodium chloride. It has alkaline reaction 
and is precipitated by alcohol as an uncrystallizable sirup. 
