300 
ELEMENTARY CHEMICAL MICROSCOPY 
EXPERIMENTS. 
a. Addition of Chloroplatinic Acid (platinum chloride) to a solution of a 
potassium salt (KCl). Application: testing for K, NH4, Rb, Cs, Na, many organic 
bases, etc. 
Repeat the experiment, using a fragment of CsCl in a drop of the same size 
as that of the potassium salt just employed. Note the instantaneous forma¬ 
tion of a precipitate and that crystals are very much smaller. Repeat again, using 
a very dilute solution of CsCl. Next try a solution drop of KCl containing very 
little CsCl. Allow to evaporate spontaneously after the addition of the reagent, 
Cs separates first, then K. 
h. Addition of Potassium Mercuric Thiocyanate to a dilute solution of a copper 
salt. 
II. The substance to be tested is added to a drop of the 
reagent. 
This method of applying tests is the one least often employed. 
It will prove successful in such reactions as require for the sepa¬ 
ration and characteristic development of the crystalline phase a 
constant addition of one component, in this case that to be 
tested for in small but almost uniform amount. 
The fragment of material is added to the center of a shallow 
broad drop. Warming gently will accelerate the separation of 
crystals. 
EXPERIMENTS. 
a. To a drop of a solution of Bi2(S04)3 containing a trace of free HNO3, add 
a fragment of K2SO4. 
Applications — Testing for K, for Na, for Bi, etc. 
III. A tiny fragment of the solid reagent is added to a drop of the 
solution of the substance to be tested. 
This case is substantially similar to Method II, and is governed 
by the same general conditions. It will be found to be the safest 
procedure in nearly all reactions where the solid phase at first 
formed is soluble in excess of the reagent, for there will always be 
during an appreciable time (owing to the rather slow solution of 
the reagent) a zone in which the equilibrium is such that the solid 
phase can exist. Thus the fragment of reagent will be surrounded 
by a clear space or ring, at the outer edge of which the solid 
