161 



The Destruction of Platinum Crucibles Through the 

 Ignition of Magnesium Ammonium Phosphate. 



By Robert E. Lyons. 



Platinum is not oxidized in the air at any temperature, nor attacked 

 by any single acid, yet there are many substances that attack and combine 

 with it at comparatively low temperatures. 



It sometimes happens that a platinum crucible is cracked or is fused 

 through during the burning of the filter paper containing magnesium am- 

 monium phosphate, or during the final ignition required to convert mag- 

 nesium ammonium phosphate into magnesium pyrophosphate. This has 

 again and again been a source of annoyance and expense to the phosphate 

 analyst. The break down of the crucible is not due to invisible mechanical 

 defects in the crucible, nor to the quality of the platinum or platinum al- 

 loy used in its construction. The cause of these occasional accidents is to 

 be found in the reduction of the phosphate through incorrect procedure in 

 burning or igniting the paper in connection with the precipitate, or, indi- 

 rectly and less frequently, by failure to observe the well-established condi- 

 tions for properly precipitating and washing magnesium ammonium phos- 

 phate. 



The direction for the treatment of the magnesium ammonium phos- 

 phate residue given in the texts and handbooks, at the disposal of the 

 writer, is by no means sufficient to enable the inexperienced operator to 

 safely use a platinum vessel in this operation. The notes on the use and 

 care of platinum ware, published by Baker & Co., Heraeus and other 

 platinum smiths, do not suggest the possibility of a mishap from the igni- 

 tion of magnesium ammonium phosphate in a platinum crucible. The notes 

 furnished by the Baker Co. have long contained the statement : "Organic 

 matter containing phosphorous should not be ignited in platinum dishes, 

 as it affects the platinum seriously." This "serious affect" is the same as 

 that noticed occasionally in connection with the ignition of magnesium 

 ammonium phosphate in platinum crucibles, and is caused by the combina- 

 tion of reduced phosphorous with the platinum, forming platinum phosphide. 



