IRON AND ALKALINE EARTH GROUPS NICKERSON. 97 



5. Procedure. Divide the above solution into two parts, 

 and to one add an excess of HC 2 H 3 2 and a few cc. of 

 Pb(C 2 H 3 O. ; ) J j solution. A yellow precipitate indicates Cr. 

 To the other portion add an excess of dilute H Cl, and then a 

 slight excess of NH 4 OH. Warm and set aside. A white 

 flocculent precipitate is A1(OH) 3 . 



6. Treatment of filtrate from 1. Acidify a small por- 

 tion of the solution with dilute HN0 3 and test for P 4 7// ions 

 with (N H 4 ) 2 Mo0 4 If a yellow precipitate is formed, treat 

 the remainder of the solution with H 2 S. A white precipitate 

 is ZnS. If no P0 4 7// ions are found, see 7. 



Notes. 1. The addition of even a slight excess of NH4OH in 

 1, is sufficient to convert the Zn into the soluble complex compound 

 Zn(NH 3 ) 4 (OH) 2 , which passes through into the nitrate and is 

 removed by H 2 S. 



2. If the addition of (NH 4 ) 2 MoO 4 shows the presence of PO/" 

 ions, then the solution after the removal of Zn contains only the 

 metals of the alkali group. 



7. Procedure. If P 4 /7/ ions are not found in 6, add 

 solution to nitrate from 3, warm, and to the warm solution 

 add an excess of H 2 S. Filter : 



Notes. 1. If P O 4 '" ions are not found in 6, the solution will 

 contain only those ions in excess of what was necessary to combine 

 with the PO 4 '" ions precipitated in 1. They may consist of: Zn, 

 Mn, Ni, Co, Ba, Sr, Ca, Mg, K and Na. 



8. Procedure. Treat precipitate with a small amount of 

 dilute H Cl (1 part H Cl 1.12 to 5 parts water) . Kesidue may 

 be Ni S and Co S. Separate in usual way. Treatment of 



