163 



1. Precipitate the magnesium with sodium hydrogen phosphate, or 

 with ammonium sodium hydrogen phosphate, rather than with ammonium 

 phosphate. 



2. Do not neglect to wash the precipitate with water containing one- 

 fourth its volume of cone, ammonium hydroxide until the washings show 

 but a faint turbidity with silver nitrate acidified with nitric acid. If 

 ammonium phosphate is present thorough washing is particularly im- 

 portant. 



3. Remove the main portion of the residue from the paper before in- 

 cinerating, or burn the paper with a small residue, in the crucible, over a 

 very small Bunsen flame. This may be quickly accomplished in a draught 

 produced by tilting the 1?& of the crucible. Do not ignite strongly nor heat 

 to the fusing point of the phosphate until the material in the crucible is 

 white (carbon free). If the ashing of the paper has been imperfect, allow 

 the crucible to cool, moisten the residue with a few drops of cone, nitric 

 acid, cover the crucible with the lid, carefully evaporate the acid and heat 

 again in the Bunsen flame. The process must be repeated until the residue 

 becomes white. 



4. To the residue in the crucible add the main portion of the pre- 

 cipitate and heat in the Bunsen flame gently at first, or untii the greater 

 part of the ammonia has been expelled, then heat strongly in the blast 

 flame until the material ceases to decrease in weight. 



