284 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 276. 



Potassium bismuth sulphate 3 K 2 SO 4 Bi 2 (SO 4 )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 7, page 251. 



In a few seconds, colorless, highly refractive, clear-cut crys- 

 tals of potassium perchlorate KCICX 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 per chlorates 

 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 little 



