MICROCHEMICAL REACTIONS OF THE COMMON ELEMENTS 367 



Upon obtaining a yellow precipitate, decant the supernatant 

 liquid, convert the double nitrite into the chloride, nitrate or 

 sulphate and test for cobalt by Method A . 



EXPERIMENTS. 



These have already been tried under Lead, Method C, page 329 (q.v.). 



C. Other Tests for Cobalt. 



As ammonium cobaltous phosphate NELiCoPC^ 6 H 2 ; 

 isomorphous with the magnesium, nickel x and manganese am- 

 monium phosphates. See Magnesium, Method J5, page 304. 



Add hydrogen peroxide and warm. The cobalt compound 

 turns brown. 



THE QUALITATIVE ANALYSIS OF MATERIAL OF UNKNOWN 

 BUT OF SIMPLE COMPOSITION. 



The following brief outline may serve as a guide to the steps 

 to be taken in the microchemical analysis of the simple " un- 

 knowns" which will be given to the student for practice. 



1. Examine the material with a low power. 



2. If found to consist of several components, try to isolate 

 them, using forceps, or scraping off particles with a knife point, 

 a file or a tiny drill. 



3. Test solubilities in water, HNOs, and NELiOH and note 

 whether the solutions obtained yield crystals on evaporation. 



4. Subject the crystalline material to polarized light and deter- 

 mine whether it is isotropic or anisotropic. If the latter, whether 

 it exhibits parallel or oblique extinction. This should afford 

 a clue as to the probable nature of the salts obtained. 



5. Add a drop of dilute HC1 presence or absence of Pb, 

 Ag, Hg, (Cu). Decant, and test solution as in 6. To residue 

 add NH 4 OH. 



6. Add a drop of dilute H 2 SO 4 presence or absence of Ca, 

 Sr, Ba, Pb, Ag, Hg, (Sb, Bi), and salts of low solubility. 



7. Add to a drop, a drop of ammonium mercuric sulpho- 

 cyanate presence or absence of Zn, Cu, Cd, Co, Fe, (Ag), (Pb), 

 (Au), (Mn). 



