142 CONTRIBUTIONS TO CHEMISTRY AND MINERALOGY. [hull. 167. 
under renewed portions of absolute alcohol. After standing several 
hours under absolute alcohol it is filtered off and dried in vacuo over 
sulphuric acid. The yield in each case is about 90 per cent of the 
theoretical, the remainder being lost in the alcoholic solution. 
Pentametaphosphimic Acid. 
/NH.POOH.NH.POOH. 
POOH< >NH. 
^XH.POOH.NH.POOH/ 
This is the lactam of amidotetrimidojyentapltosphoric acid, 
.OH 
/NH.POOH.NH.PO< 
POOR< \nh 2 
\NH.Poorum.po(OH) 2 
It exists in the lactam form in the 5-atom silver salt and apparently 
in the solution of its acid and normal salts; in alkaline solutions, 
however, it has probably the open form, as the silver salt prepared 
from such a solution has a composition corresponding to this. 
The free acid may be obtained, somewhat contaminated with decom- 
position products, by decomposing the silver salt under water by hydro- 
gen sulphide, care being taken to keep the liquid cool. The solution 
has an acid, somewhat astringent, taste, and is imperfectly precipitated 
by alcohol in a gelatinous form, resembling precipitated alumina. This 
shows the reaction of the salts, but is impure, as caustic alkali causes 
the evolution of little ammonia. 
Sodium salts. — As all the sodium salts are amorphous and precipi- 
tated by alcohol, in a sirupy or viscous form, it is not easy to obtain 
any of them pure. The salt prepared in the above manner contains 
about 5.4 atoms of sodium (analyses 1 and 2) and forms a white, sandy, 
amorphous powder, which is not hygroscopic, but which slowly absorbs 
carbon dioxide. Under water it first becomes pasty and then slowly 
dissolves, with considerable evolution of heat. Salts with 4 or more 
atoms of sodium invariably contain 2 molecules of water which are 
retained at 100°. 
The peuta-sodium salt, Ps^OmHsNas-f 2H 2 0, may be obtained by 
adding to the solution of a salt containing a known excess of sodium 
nearly enough nitric acid to neutralize the excess and precipitating by 
alcohol, or by nearly neutralizing with acetic acid, with phenolphthalein 
as indicator, and precipitating by alcohol. In the latter case, however, 
there is a slight deficiency of sodium (analyses 3 and 4). The normal 
salt has a strongly alkaline reaction and loses some alkali by repeated 
precipitation by alcohol. 
