A PROCEDURE FOR THE QUALITATIVE 31 



Notes.— 1. Because of the reaction MgNH^PO^ + H^O = NH40H + Mg 

 HPO4, a large excess of NH4OH is used. 



2. Only the minimum quantity of H3PO4 necessary should be added. 

 Too large an excess causes the solution used in P. 7 to be too acid. The excess 

 of phosphate may be removed before carrying out P. 4 by adding hydrated 

 ferric oxide and filtering. 



3. If, at the beginning of the analysis of the iron and aluminium groups, 

 phosphates were found to be present in the sample under investigation, it 

 might be well at that point to add sufficient phosphoric acid to insure the 

 complete precipitation of the alkaline earth group and magnesium as phos- 

 phates, and then to follow the procedure as given by C. B. Nickerson in his 

 paper "Arrangement of Procedure for the Removal of Phosphate Ions from 

 the Iron and Alkaline Earth Groups" published in the Transactions of the 

 Nova Scotian Institute of Science, Vol. XIII, Part 2, pp. 95-98. 



Procedure 2. Removal of Alkaline Earths. 



Extract the precipitate from P.l with 5 c.c. of 3n. HjSO^. 

 To the extract add 10 c.c. of methylated spirits and shake for 

 a few minutes. Filter, if necessary. 



Notes. — 1. Traces of the alkaline earth group may have escaped pre- 

 cipitation as carbonates. If so, they would be precipitated in P.l by the 

 phosphate in the form of a flocculent, not granular, precipitate. There- 

 fore, the confirmatory test for magnesium should be carried out if the preci- 

 pitate formed in P.l is scanty or flocculent. 



2. The sulphates of the alkaline earth group are insoluble in an alcoholic 

 solution, though calcium sulphate is appreciably soluble in aqueous solution. 

 Methylated spirits are used rather than ethyl alcohol because of the regula- 

 tions concerning the use of the latter. 



Procedure 3. Confirmatory Test for Magnesium. 



Add to the filtrate from P.2 5 c.c. of 15n. NH^OH and 5 

 c.c. of 4n. H3PO4. Let stand at least half an hour with frequent 

 shaking. A white granular precipitate is AlgNH4P04 and 

 confirms the presence of magnesium. 



Notes. — 1. H3PO4 is used rather than Na2HP04 because the preci- 

 pitate formed in the former case is more distinctly crystalline. 



Procedure 4. Removal of Ammonium Salts. 



Evaporate the filtrate from P. 3 in a beaker until crystals 

 appear. Then transfer to an evaporating dish and evaporate 



