146 
CONTRIBUTIONS TO (JHEMIS'JKY AND MINERALOGY. 
[BOLL. 167. 
of the composition P 3 N 3 7 H2Ag 6 and P,N40 9 H 2 Ag 8 respectively. 1 These 
are salts of the open-chain acids. A similar salt is obtained by pre- 
cipitating an ammoniacal solution of pentametaphosphimic acid by 
silver nitrate, but in accordance with its less acid properties the quan- 
tity of silver does not reach 10 atoms, being in the specimen analyzed 
only 8.76 atoms, but the figures correspond closely to a derivative of 
amidotetrimidopentaphosphoric acid, Ps^OnH^, rather than penta- 
metaphosphimic acid. Dried at 100° it gave: 
Ratio P : Ag. 
P. 
Ag. 
fP5N5OuH3.34Ags.7a 
5:8.76|p 5 N 5 J oH 1 . 24 Ags. 76 
(Found 
11. 49 
11.64 
11.48 
70. 04 | 
70.98 
70.03 
It appears, therefore, that in alkaline solution the metaphosphimic 
acids become open-chain acids, just as lactones and lactams give y- and 
doxy- and amido-acids. On drying at 100°, the yellow silver salts 
become gray without loss of weight, probably owing to separation of 
silver oxide. This is perhaps due to a tendency to revert to the lactam 
form, with separation of silver oxide, rather than water. 
Decomposition of Pentametaphosphimic Acid. 
Pentametaphosphimic acid is markedly more stable in acid solution 
than trimetaphosphimic acid. In the section on the latter I described in 
detail its decomposition products when acted on by nitric acid. Under 
identical conditions the rate of decomposition of pentametaphosphimic 
acid was found to be very much slower. On account of this greater sta- 
bility the action of hot acetic acid gives more satisfactory results. No 
attempt was made to isolate all the products, as these are numerous and 
the analytical difficulties considerable. The following were identified: 
Tetrametaphosphimic acid, P,N.iO«H 8 . 
Triimidotetraphospkoric acid, P4N3O10H9. 
Diimidotriphosphoric acid, P 3 N 2 B H7. 
Orthophospkoric acid, HjPO^. 
Five parts sodium pentametaphosphimate are dissolved in 15 parts 
water, 5 parts strong acetic acid added, and the solution heated in the 
water bath. The separation of a crystalline precipitate of acid sodium 
tetrametaphosphimate begins in about fifteen minutes and continues 
for perhaps eight hours, at the end of which time the solution gives no 
precipitate with magnesium chloride, indicating the absence of penta- 
metaphosphimate. The sodium tetrametaphosphimate, being insoluble 
in a solution of sodium salts, is completely precipitated. It is filtered 
off and washed a little with saturated sodium acetate solution. The 
1 In the third section of this paper the formula P 4 N 4 () 8 Ag s was ascribed totheper-silver salt of tetra- 
metaphosphimic acid; a recalculation of the analyses in the above manner, however, shows that they 
correspond much more closely to the open form r 4 N 4 u H^Agf iJ with a slight deficiency of silver. 
