162 



The reduced phosphorous unites with platinum even ;it a dull red heat 

 (600° 0.). 



The external appearances of a crucible which has suffered such an 

 attack are characteristic. Cracks of varying length appear, usually in the 

 bottom, but sometimes in the sides; the fractured surfaces are distinctly 

 crystalline; the edges of the fractures are usually raised and puffed and 

 at times present unmistakable 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 upon 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 magnesium precipitate. 



3. 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° Oent.J Dry ammonia gas passed 

 over magnesium pyrophosphate heated to 950° Cent, yields phosphine and 

 red phosphorous.! 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 acid. Ammonium phos- 

 phate heated in a covered platinum crucible to 700-800° 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 summarized suggestions will insure 

 the safety of the platinum crucible in the ignition of magnesium ammonium 

 phosphate : 



Zeitsch. f. angew. Ch. 



