148 
CONTRIBUTIONS TO CHEMISTRY AND MINERALOGY. Tbull.167. 
them to be identical in form. The yield of tetrametaphosphimic acid 
appears to be nearly independent of proportions and concentration, 
and was about 12 per cent of that required by the equation 
P 6 N 5 OioH ] o + 2H 2 0=P4N 4 8 H 8 + NH4H 2 P04. 
Triimidotetraphosphoric acid, PO(OH) 3 .NH.PQOH.NH.POOH.NH. 
PO(OH) 2 . — The sodium salt of this, the third member of the imidophos- 
phoric acid series obtained, crystallizes well in small rhombic or six- 
sided plates. The several specimens obtained were not analyzed, but 
converted into the silver salt. By analogy with P 3 N 2 8 H 7 , there 
can be little doubt that it is the acid salt, PJ^OioHsNa^. It is easily 
soluble in water, but almost insoluble in saturated sodium acetate solu- 
tion or dilute alcohol. It gives a precipitate with magnesium nitrate 
only on adding ammonia and ammonium chloride, when a voluminous 
precipitate is obtained, which, on standing, slowly changes to minute 
crystalline spherules. 
Silver triimidotetraphosphate, P^OioIIsAg^ is obtained as a volumi- 
nous amorphous white precipitate by adding silver nitrate to a solution 
of the sodium salt faintly acidified with nitric acid. On long standing 
under its mother-liquor it becomes crystalline and this change occurs 
in a few moments on washing the precipitate, shrinking to a heavy, 
sandy, crystalline powder, a very characteristic behavior. The same 
change cau be observed under the microscope in the partially washed 
salt, the amorphous portion changing to minute particles showing 
active Brownian movement, which aggregate to prisms which are long 
and pointed and often tufted at the ends, and which can not be dis- 
tinguished in appearance from silver tetrametaphosphimate. From a 
decidedly acid solution the salt is deposited slowly and without the 
intermediate amorphous form. 
The salt gave after drying at 100° : 
Calculated for 
P4N 3 O 10 H 5 Ag 4 . 
Found. 
1. 
2. 
p 
16.26 
5.52 
56. 58 
16.43 
5.62 
56.61 
16.48 
5.55 
57.18 
N 
As 
1. P:N:Ag: 
2. P:N:Asr 
4:3.03:3.96. 
4:2.98:3.99. 
Triimidotetraphosphoric acid could not be obtained from tetrameta- 
phosphimic acid, being much less stable than the latter. It is therefore 
probably derived from the breaking down of the chain of phosphorus 
and nitrogen atoms formed by the hydrolysis of the pentametaphosphi- 
mic ring. 
