MICROCHEMISTRY. 67 



tetragonal pyramids at ordinary temperatures, but in the 

 monoclinic form in a boiling solution. 



2. Fresh sections are placed directly in a solution of am- 

 monium carbonate ; if calcium is present, small, strongly 

 doubly refractive rhombohedra of calcium carbonate are 

 formed within the cells. If the cell-sap is strongly acid, it 

 .should first be neutralized with ammonia. 



13. Magnesium, Mg. 



100. Schimper recommends (II, 214) the addition to the 

 sections or to the ash, for the recognition of magnesium, 

 of a solution of sodium phosphate or of microcosmic salt 

 (NaNH 4 HPO 4 ) reduced with a little ammonium chloride. 

 There are then formed rhombic crystals of ammonio-mag- 

 nesium phosphate (MgNH 4 PO 4 ) which have in sections the 

 form of coffin-lids, but in the ash are chiefly the X-shaped 

 skeletons (cf. Fig. 20, 77). 



Uranyl acetate causes, if sodium is also present, the forma- 

 tion of the crystals of magnesium-sodium-uranyl acetate, 

 already referred to (cf. 83). 



101. Magnesium oxalate , Mg(COO) 2 . Monteverde (I) 

 found, in the epidermis of fresh leaves of Setaria viridis and 

 in dried leaves of numerous Panicece, radially striped sphae- 

 rocrystals or irregular aggregates, which probably consist 

 of magnesium oxalate. These were, according to his state- 

 ments, with difficulty soluble in water, insoluble in acetic 

 acid, and soluble in hydrochloric, nitric, and sulphuric acids, 

 in the latter without formation of gypsum needles. After 

 the addition of an ammoniacal solution of sodium phosphate 

 and ammonium chloride, crystals of ammonio-magnesium 

 phosphate were formed ; after heating, these dissolved with- 

 out evolution of gas ; gypsum-water caused the formation of 

 calcium oxalate crystals ; and after treatment with caustic 

 potash solution the sphaerocrystals lost their striping and 

 double refraction and became soluble in acetic acid. 



Magnesium phosphate (MgO 2 ) 3 (PO) 2 ? According to Han- 

 sen (I, 115), crystals of magnesium phosphate are precip- 

 itated in the stem of the sugar-cane by alcohol. These 



