310 
ELEMENTARY CHEMICAL MICROSCOPY 
ing or coloring can be quickly and simply accomplished, advan¬ 
tage should at once be taken of the fact. 
As examples of qualitative tests which may be considered as 
falling under this method, the following may be cited: 
In testing for perchlorates, the addition of a permanganate 
will yield colored perchlorate crystals. 
Iodine and bromine are revealed by their coloring starch 
granules, or the presence of a compound setting free iodine from 
an iodide or from an iodate is ascertained by starch. Or, on the 
other hand, starch is easily differentiated from other substances 
by staining with an iodine solution. 
Most oil or fat globules may be stained by alkanin. 
Fullers earth affords a simple means of distinguishing between 
vegetable and aniline dyes and in a few cases between certain 
aniline dyes themselves. 
In the microchemical examinations of rock sections, aluminum 
hydroxide can be stained with congo red and gelatinous silica 
with malachite green — tests which may be employed in testing 
for “weathering,” etc. 
EXPERIMENTS. 
a. Next to a drop of a dilute solution of HCIO4 or NH4CIO4, place a drop 
of RbCl solution (or KCl, if no Rb is obtainable). Cause the Rb to flow into 
the perchlorate (Method I). In a few seconds colorless, characteristic crystals of 
RbC104 separate. Place a drop of dilute KMn04 next to the preparation and 
cause it to flow into it. The crystals of RbC104 will become colored pink. The 
resulting compound is a solid solution (isomorphous mixture) of the permanganate 
in the perchlorate, due to adsorption. 
h. To a drop of a dilute KI solution add a few granules of potato or arrow-root 
starch. Stir. Examine under the microscope. Add at the center a very minute 
fragment of pure KNO2 or NaNOa. Examine again. The starch granules should 
appear at the most only very slightly colored. Add a trace of very dilute HC2H3O2 
or H2SO4. The starch granules turn blue or purple, due to adsorption of liberated 
iodine. 
Repeat the experiment, substituting a bromide for the iodide and (NH4)2S208 for 
the KNO2 
i X. The reagent dissolved in a volatile solvent is spread in a film 
upon an object slide in such a manner as to yield a coating or varnish 
non-crystalline in character, and across this prepared surface a 
solution of the unknown material is drawn. 
