stokes.] TRIMETAPHOSPHIMIC ACID. 93 
formula, and that the acid is the symmetrical inner anhydrid or lactam 
of an open chain acid, we may regard this salt as being formed by 
addition, thus: 
PO.ONa 
PO.ONa 
HN NH 
UN NH 2 
| | + NaOH = 
D.PO PO.ONa 
\ / 
N 
Na0 -^/°<ONa 
N 
H 
H 
the latter being a salt of amido-dihnidotriphosphoric acid.' Unfortu- 
nately I have been unable to prove this with certainty. A silver salt 
of the composition P 3 N 3 7 H4Ag4 would render it extremely probable, 
as all silver salts of phosphorus nitrogen acids hitherto observed 
are free from crystal water. A salt with 4 atoms of silver can be 
obtained from the above 4-atom sodium salt, but it is very unstable, 
and its composition does not agree with sufficient sharpness with that 
of the cyclic or open chain form to establish either formula definitely. 
I am therefore inclined to give preference to formula (b). It seems 
likely, however, that salts of triphosphonitrilic acid may also exist. 
The hexa-silver salt has been observed in two well-defined forms, as 
well as a third, possibly intermediate one. One of these is white, 
amorphous, and soluble in ammonium nitrate. It is easily converted 
into the other of identical composition, which is red, crystalline, and 
insoluble in the same reagent. The colorless salt probably contains 
silver united to oxygen only, while in the other one-half is united to 
nitrogen. 
Decomposition products of trimetaphosphimic acid. — An aqueous solu- 
tion of trimetaphosphimic acid, or of one of its salts acidified with one 
of the stronger mineral acids, decomposes slowly in the cold, rapidly on 
heating, the ultimate products being orthophosphoric acid and ammonia. 
If, however, the action be limited, there results a mixture of interme- 
diate acids. The analysis of this mixture, which involved many 
experimental difficulties, proved the presence of the following: 
1. Unchanged trimetaphosphimic acid, P 3 N 3 6 H 6 . 
2. Diimidotriphosphoric acid, P 3 N 2 8 H7. 
3. Imidodiphosphoric acid, 2 P^NOoHs. 
4. Pyrophosphoric acid, P 2 7 H 4 . 
5. Orthophosphoric acid, PO ( H 3 . 
'T1h> acids P0(0H) 2 .0.P0(0H) 2 and P0(0H) 2 .0.P0(0H).0.P0(0H) 2 being frequently designated 
as di- and triphosphoric acid, I call those in which the linking oxygen is replaced by imide, Nil, 
imido-di- and diimidotriphosphoric acid. 
2 Thisacid has the same composition and is probably identical with Gladstone's azophosphoric or 
pyrophosphamic acid. Jour. Chem. Soc. London [2J, Vol. VI, p. 66, etc. 
