162 
The reduced phosphorous unites with platinum even at a dull red heat 
(600° C.). 
The external appearances of a crucible which has suffered such an 
attack are characteristic. Cracks of varying length appear, usually in the 
bottem, but sometimes in the sides; the fractured surfaces are distinctly 
crystalline; the edges of the fractures are usually raised aud puffed and 
at times present ummistakable signs of fusion. 
Reduced phosphorous, the immediate cause of the destruction of the 
crucible, may be accounted for by inquiry into the nature, the origin and 
the conditions governing the deportment of reducing agents which could 
act upoh magnesium ammonium phosphate during the processes of incin- 
eration and ignition. 
The reduction of the phosphate may be due to any or all of the fol- 
lowing: 
1. Carbon from the imperfectly ashed filter paper. 
2. Ammonia liberated by heat from magnesium ammonium phos- 
phate, or from sodium ammonium phosphate, or ammonium phosphate, 
which may be present in abnormal amount in the maghesium precipitate. 
5. Hydrogen from the dissociation of ammonia at the high tempera- 
ture, and also from the incomplete combustion zone of the gas flame by 
diffusion through the platinum crucible. 
The reduction of magnesium pyrophosphate by carbon begins at 950° 
Cent. and becomes violent at 1,100 to 1,200° Cent. The reduction by 
hydrogen begins somewhat below 900° Cent. Dry ammonia gas passed 
over Magnesium pyrophosphate heated to 950° Cent. yields phosphine and 
red phosphorous.t The destruction of the platinum vessel is most rapid 
when the residue contains free ammonium phosphate, which upon fusion 
yields most of its ammonia and meta-phosphoric aeid. Ammonium phos- 
phate heated in a covered platinum crucible to TOO-S00° Cent. causes com- 
plete destruction of the vessel. Holes appear in the bottom and sides, and 
the lid may fuse. ‘The quantity of ammonia from the magnesium am- 
monium phosphate, which has been properly prepared, will prove destruc- 
tive only under especially unfavorable conditions, e. g. very rapid heating 
of the phosphate to a high temperature. 
Strict observance of the following suminarized suggestions will insure 
the safety of the platinum crucible in the ignition of magnesium ammonium 
phosphate : 
Zeitsch. f. angew. Ch. 
