342 
ELEMENTARY CHEMICAL MICROSCOPY 
Tetragonal. 
Orthorhombic. — Chromate (0 or M). 
Monoclinic. — Chloride; chlorate; bromide; ferro- 
cyanide; acid-oxalate. 
Triclinic. — Acetate. 
DETECTION. 
A. By Means of Sulphuric Acid. 
Read fully the directions and comments under Calcium 
and Strontium, pages 335 and 336, and 339 and 340. 
The amorphous or semicrystalline precipitate first obtained 
must be recrystallized from concentrated sulphuric acid before 
identification is possible. The recrystallized salt appears at 
first as tiny rectangular plates and X-like crystallites. In this 
stage of development it may be mistaken for strontium sulphate. 
Continue breathing upon the drop of acid; under the influence 
of the moisture absorbed the crystallites grow rapidly, still 
retaining their X-like shape but the arms of the X’s become 
feathered. There is a marked tendency for two adjacent arms 
of the X to develop much more rapidly than the other two. 
These crystalUtes grow relatively large and are constant and 
peculiar to barium. 
In the presence of certain acids or acid salts, especially from 
hot solutions, crystallites of barium sulphate may sometimes be 
obtained immediately upon the addition of dilute sulphuric acid. 
In the event of a heavy precipitate being obtained with the 
reagent, it is wise to remove a small portion to another slide for 
crystallization, rather than attempt to dissolve the whole mass. 
Recrystallization in the presence of much calcium is to be 
avoided. First extract the calcium sulphate with hot water. 
In the presence of moderate amounts of strontium the crys¬ 
tallites of barium sulphate are generally not well formed. If 
strontium is in excess, the crystals separating from the hot sul¬ 
phuric acid have the general type of strontium sulphate, but are 
not well developed and exhibit an inclination to approach the 
X-forms of barium sulphate. For this reason it is advisable to 
remove any strontium which may be present by repeatedly 
