338 
ELEMENTARY CHEMICAL MICROSCOPY 
changing to crystals of a great variety of forms, hexagonal 
plates, six-sided plate-like prisms and stout prisms with obliquely 
truncated ends. 
In the presence of stannic chloride Behrens has shown that 
calcium oxalate assumes the form of tiny oval grains exhibiting 
an octahedral tendency while strontium yields large clear-cut 
beautifully developed tetragonal octahedra and barium gives 
short stout prisms singly, in crosses and in radiating masses, 
or if much barium is present, fusiform crystals and bundles of 
radiating needles are seen. 
Precautions. 
Oxalic acid, under favorable conditions, can cause the separa¬ 
tion of oxalates of the following elements: Gl, Ca, Sr, Ba, Mg, 
Zn, Cd, Tl; rare earths; Sb, Bi, Sn, Pb, U, Mn, Fe, Ni, Co, 
Cu, Ag. 
In the event of a precipitate of doubtful composition being 
obtained, draw off the supernatant liquid, or separate by means 
of the centrifuge, and add to the residue a tiny drop of dilute 
sulphuric acid; calcium oxalate is dissolved and in a few seconds 
the characteristic crystals of CaS04 • 2 H2O make their appear¬ 
ance. 
Owing to the minute size of the crystals, testing for calcium 
with oxalic acid is not always satisfactory. As an offset to this 
disadvantage, chlorides of the trivalent metals, unless in con¬ 
centrated solution, and boric acid have no effect other than a 
retardation of the reaction. A small amount of free nitric acid 
merely greatly retards the separation of the oxalates of calcium 
and strontium, but prevents the formation of barium oxalate. 
EXPERIMENTS. 
a. Try reaction after the manner given above, on a salt of Ca in a neutral solution. 
Try again in the presence of free HCl, then in the presence of free HNO3. 
b. Precipitate CaC204 • 3 H2O, draw off the supernatant liquor and treat the residue 
with dilute H2SO4. After examining the preparation, add more acid, and heat 
until white fumes appear; cool; breathe upon the preparation and examine again. 
STRONTIUM. 
Crystal Forms and Optical Properties of Common Salts 
of Strontium. 
