92 CONTRIBUTIONS TO CHEMISTRY AND MINERALOGY. [bull. 167. 
ride and ammonia is best explained on this assumption, as is its 
decomposition into ortliophosphoric acid and ammonia. If phosphorus 
were united to phosphorus and nitrogen to nitrogen, the formation of 
reducing phosphoric acids or of hydrazine might be expected. Neither 
is it likely that chlorine is united to nitrogen, for in this case hydroxyl- 
amine might be expected to result. Several structural formulas are 
possible which meet this requirement, the simplest being that in which 
the nucleus consists of a symmetrical ring of 3 phosphorus and 3 
nitrogen atoms : 
PCI* 
N N 
II I 
CI 2 P POL 
\ S 
N 
or a similar one with diagonal or " centric" union. 
Direct replacement of chlorine by hydroxyl would then give 
P(OH), 
/ \ 
N N 
II I 
(HO) 2 P P(OH) 8 
\ S 
* N 
(a) 
Triphosplionitrilic acid. 
The labile nature of the hydrogen atoms in nitrogenous bodies, as 
observed in many organic compounds, makes it by no means improbable 
that an acid of this form may of itself, or under the influence of 
reagents, undergo transformation into the tautomeric form : 
PO.OH P.OH 
/A\ 
HN NH HN O O NH 
II \/ \| 
HO.PO PO.OH or HO.P — O — P.OH 
\ / \ / 
N N 
H H 
(b) (o) ^ 
Trimetaphospbiiuic acid. 
An acid of the form (a) may be expected to give two sodium salts in 
which, respectively, 3 and 6 atoms of hydrogen are replaced. A salt 
with 6 atoms of sodium can not be produced, however, by any method 
which I have tried. The only salt besides the ordinary one with 
3 atoms of sodium is one with 4 atoms, and this is formed in the 
presence of a large excess of caustic soda; it is very unstable and is 
reconverted into the 3-atom salt by repeated precipitation from aque- 
ous solution by alcohol. It is not obvious why an acid of the form (a) 
should give such a salt. If we assume that (b) represents the correct 
