MICROCHEMICAL REACTIONS OF CALCIUM 
337 
c. Precipitate with dilute H2SO4, then heat, adding more acid if necessary, until 
white fumes are given off, cool, breathe on the preparation and examine. Calcium 
will separate either as the salt CaS04, or as CaS04-H2S04. The crystal forms 
most frequently met with are thin, rounded, prism-like plates or fusiform crystals 
with tufted ends. This modification of the test is not satisfactory for Ca, but is 
characteristic for Ba and for Sr (q.v.). 
d. Try testing for a trace of Ca in the presence of a large quantity of salts of 
the elements of Group I. A retardation of the reaction results. 
e. Try effect of a solution of (NH4)2C03 on crystals of CaS04- 2 H2O. 
B. By Means of Oxalic Acid. 
Apply the reagent according to Method /, page 299. 
The oxalate which separates at room temperature from neutral 
or slightly alkaline solution has the formula CaC204 • 3 H2O, 
and belongs to the tetragonal system. The crystals are tiny, 
highly refractive octahedra, or rectangular or square plates. If 
rapidly formed, crosses and bundles or sheaves of crystallites 
will be seen. From hot or acid solutions a monoclinic oxalate 
CaC204 • H2O separates which is practically valueless as an 
identity test for calcium. This same salt appears to sometimes 
separate if a large excess of oxalic acid has been added. In addi¬ 
tion to changing the crystal form free mineral acids so increase 
the solubility of calcium oxalate as to sometimes prevent its 
precipitation. 
Strontium gives with oxalic acid an identical reaction, save that 
the crystals of strontium oxalate are generally somewhat larger. 
Barium oxalate takes the form of fibrous bundles of needles 
and is not likely to be mistaken for either calcium or strontium. 
Zinc under certain conditions may yield a zinc oxalate difficult 
to distinguish from the oxalates of calcium and strontium. 
Magnesium oxalate will separate in forms not to be distin¬ 
guished from calcium oxalate if the test drop contains much 
acetic acid, but in the absence of this acid magnesium oxalate 
will not appear. 
Manganese forms groups of radiating needles (see Manganese). 
Lead oxalate may also assume forms somewhat resembling 
those of calcium oxalate, but after a short time these crystals 
grow into large, well-developed prisms. 
Silver oxalate separates first as a granular deposit, soon 
