228 



r>. A yellow precipitate proves the presence of potassium in the sohi- 

 tion (ammonium compounds must be absent). 



1. To the remainder of filtrate I add an excess of perchloric acid'. 

 A white crystalline precipitate of potassium perchlorate is formed. Fil- 

 ter (II) and test a few drops of filtrate II with the sodium cobaltic ni- 

 trite. If a precipitate is formed, add to the filtrate II more perchloric 

 acid, filter again and test as above, \yhen the sodium cobaltic nitrite 

 shows that all potassium has been removed by the perchloric acid, proceed 

 as directed in B, 2, for the detection of sodium. 



2. To the filtrate from B, 1, add a few drops of hydrofluosilicic acid, 

 H=SiF". A cloudy flocculent precipitate indicates the presence of sodium 

 in the solution. This precipitate is not very voluminous and must be 

 looked for carefully if only a little sodium is present. Tnrn the test tube 

 and examine the sides for adhering precipitate. 



This method has been trietl in this laboratory with excellent results 

 Some of the advantages are: 



1. JMaguesium does not interfere and nee<l not be removed. Mag- 

 nesium pcrclilorate is very sttlulile. Magnesium tluosilicate is soluble and 

 only precipitated, even in the alcolu)] solution. wIumi large amounts are 

 present. 



2. The test for sodium is delicate liut traces of swlium which are 

 present in so many rcai^cnts arc not detected. This is an advantage over 

 the spectrum test where all sul)Stances show sodium. 



3. The tests are simple and easily understood an<l followed by the 

 students. 



4. The tests are decisive and tiie student has confidence in his work. 

 n. Only a short time is nHjuirwl to make a test. 



2 Tho percliloric acid must be free from sodium but thn prosonco of potassium 

 does no harm bocanso potassium is detected previously, by the use of sodium co- 

 baltic nitrite, and any potassium present is precipitated by the alcoholic perchloric 

 acid solution. 



/ iidia na Uni rcrsiti/, 

 Bloomlngton, IiuUana. 



