330 
ELEMENTARY CHEMICAL MICROSCOPY 
B. By Means of Bismuth Sulphate. 
For method of applying the test and discussion of the prop¬ 
erties of the salt formed see Test B under Sodium, page 322. 
Potassium bismuth sulphate 3 K2SO4 • 612(804)3 separates first 
as circular disks which later develop into hexagonal plates or the 
skeletons of hexagons, i.e., six-pointed stars and rosettes. 
Ammonium salts yield similar crystals. Hence this test can¬ 
not be used to differentiate between potassium and ammonium. 
Precautions. 
See Sodium, Method B. 
EXPERIMENTS. 
See Sodium, Method B. 
C. By Means of Perchloric Acid. 
Apply the reagent by Method /, page 299. 
In a few seconds, colorless, highly refractive, clear-cut crys¬ 
tals of potassium perchlorate KCIO4 separate. These crystals 
belong to the orthorhombic system, but at first sight those first 
formed usually appear to be isometric, while later, forms which 
might be mistaken for monoclinic prisms appear. 
Rubidium and cesium give a like reaction, and their per¬ 
chlorates are more insoluble than that of potassium. Thallium 
forms an even more insoluble perchlorate. The perchlorates 
of the elements of the other groups that are generally met with 
in ordinary work, are sufficiently soluble not to interfere.' 
Potassium, rubidium, and cesium perchlorates possess a re¬ 
markable adsorptive power for potassium permanganate. The 
crystals are not altered in habit, size or rapidity of formation but 
become colored rose or rose-violet. The compounds resulting 
are a solid solution of potassium permanganate in the per¬ 
chlorates and are considered by crystallographers to be iso- 
morphous mixtures of the two salts. 
Advantage may be taken of this property of the potassium 
salt to obtain an exceedingly beautiful test, for if the test drop 
contains sodium permanganate, the potassium perchlorate sepa¬ 
rating therefrom will be colored. Add to the test drop a httle 
