MICROCHEMICAL REACTIONS OF MAGNESIUM 
351 
The detection of magnesium in simple salts is comparatively 
easy and rapid, since characteristic crystals are readily obtained, 
but its microchemical identification in complex mixtures is usu¬ 
ally a matter of not a little difficulty, in as much as this element 
is commonly associated with others, closely related, which are 
prone to interfere with or prevent the formation of typical 
crystals with the reagents employed for its recognition. 
Two methods are available, the choice of procedure depending 
upon the nature of the salts present in the drop to be tested. 
In all cases where there is a doubt as to the probable composition 
of the material to be examined, it is best to have recourse at 
once to the modification II.^ 
I. To the solution of the material to be tested, which must 
not be too concentrated, add several fragments of ammonium 
chloride; stir; then add a very slight excess of ammonium hy¬ 
droxide, and warm the preparation. (If a precipitate results it 
is best to draw off the clear solution.) To the warm solution add a 
small crystal of secondary sodium phosphate. Crystals of am¬ 
monium magnesium phosphate NH4MgP04 • 6 H2O soon appear. 
II. To the solution to be tested add a fragment or two of 
citric acid, stir until dissolved, then add an excess of ammonium 
hydroxide. Evaporate to dryness. To the residue add dilute 
ammonium hydroxide. Warm; then add a very small frag¬ 
ment of secondary sodium phosphate. Crystals of ammonium 
magnesium phosphate separate. 
The crystals of the ammonium magnesium phosphate sepa¬ 
rate as skeletons and hemimorphic forms of the orthorhombic 
system (see Ammonium). 
It should be remembered that a number of elements are 
precipitated by phosphates in alkaline solution; the most fre¬ 
quently met with in the course of microchemical analyses, either 
in the substance to be tested, or present as reagents from previous 
tests, are, doubtless, lithium, members of the calcium and mag¬ 
nesium groups, trivalent metals, manganese, nickel, cobalt, tin, 
lead, silver, copper, and uranium.^ Of these elements, lithium, 
^ Romijn, Zeit. anal. Chem., 37 , 3.00. 
“ Most of these elements wiU generally have been removed in the progress of 
the analysis before the addition of the sodium phosphate. 
