MICROCHEMICAL REACTIONS OF THE COMMON ELEMENTS 285 



sodium manganate, 1 so as to impart a distinct green, then add 

 a tiny drop of hydrochloric acid, thus converting the manganate 

 into permanganate. The perchloric acid is then caused to flow 

 in. The crystals of potassium perchlorate which separate have 

 the same form as before, but are a beautiful deep rose color, the 

 color intensity varying with the amount of permanganate present. 

 In a few moments the liquid is completely decolorized, and the 

 precipitated crystals deeply colored. Performed in this way the 

 test is a most interesting and instructive one. 



The perchlorate reaction is of more value for the detection of 

 the acid by means of rubidium chloride and for the removal of 

 potassium to prevent interferences with tests for other elements, 

 than for the identification of potassium. 



Precautions. 



To obtain truly satisfactory results, careful attention to con- 

 centrations must be given, for if the solution is too concentrated 

 potassium perchlorate is precipitated at once in malformed or 

 skeleton crystals; while if too dilute the separation of the solid 

 phase is too slow. 



Exposure to alcohol vapor hastens the reaction. 



In the absence of perchloric acid ammonium perchlorate may 

 be used. 



EXPERIMENTS. 



a. Try the above reaction with different salts of K. 



b. Introduce NaMnO 4 into the test drop, and test as above. 



c. Make a mixture of K and Na salts. Treat a drop of a solution of this mate- 

 rial with HC1O 4 , evaporate, treat with the reagent again and again evaporate, 

 extract the dry residue with alcohol, and test the alcoholic extract for sodium with 

 U0 2 (C 2 H 3 2 ) 2 . 



d. Try the action of HC1O 4 on members of the magnesium group, and upon 

 members of the calcium group. 



AMMONIUM. 



Crystal Forms and Optical Properties of Common Salts 

 of Ammonium. 



1 Sodium manganate is employed instead of sodium permanganate because it 

 is more stable as a laboratory reagent. 



