414 ELEMENTARY CHEMICAL MICROSCOPY 



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 375 (q.v.). 



C. Other Tests for Cobalt. 



As ammonium cobaltous phosphate, NH4C0PO4 -6 HoO; 

 isomorphous with the magnesium, nickel and manganese ammo- 

 nium phosphates. See Magnesium, Method B, page 350. 



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 is intended to serve as a guide to the steps to be taken in a 

 preliminary analysis of inorganic materials. It is merely a suggestion of some of the many 

 methods whereby we may obtain a rough idea of the nature of the material in question 

 and may thus be enabled to more judiciously apply identification tests. 



t. The substance is a liquid. Test its reaction toward litmus-silk. Evaporate a portion 

 to dryness; note well any tendency to decomposition or to hydrolysis. Do not forget 

 that volatile constituents may have been expelled due to the evaporation. Treat the resi- 

 due as suggested for solids. 



2. The substance is a solid, (a) If an alloy test it with a needle or a knife blade for its 

 hardness, ductility, etc.; dissolve a fragment in HNO3, HC1, or aqua regia as the material 

 may require; evaporate this acid solution to dryness to drive off the excess of acid; take 

 up the residue in a drop of acidulated water and proceed as outlined below, (b) Under 

 the microscope the substance appears to consist of several components. Try to isolate 

 them by picking out with a moistened glass rod, a platinum wire, a dissecting needle or with 

 fine forceps; test each fragment in turn; always examine first between crossed nicols. 

 (c) Heat a particle on the corner of an object slide or upon a nickel or platinum spatula. 

 Note carefully its behavior. 



3. Test for solubility in water; in HC1; in HNO3. If completely insoluble in these sol- 

 vents, treat as in 18 below. If the material is an alloy which may contain Sn, evaporate 

 repeatedly with HXO3 to render the Sn insoluble. 



4. If the material appears to consist of a salt or a mixture of salts soluble in water, try 

 to obtain crystals from the aqueous solution and observe their habit and study their behavior 

 with polarized light. Test for the acid radicals by the Bunsen-Treadwell system, pages 

 416-420. Test a drop of the aqueous solution with indicator fibers, page 309, both before 

 and after boiling. Note well what takes place. Not infrequently time may be saved 

 by testing for the acids before the bases. 



5. When the material is insoluble in water, but soluble in HC1 and HNO3, a study of 

 the crystalline salts formed upon evaporation is of less value than in the preceding case. 

 But if the crystals obtained are isotropic, the analysis becomes very simple, since there 

 are few isotropic chlorides and nitrates. 



6. If the material is insoluble in water but soluble in HNO3, it is obvious that the Bunsen- 

 Treadwell system cannot be applied in its entirety for identifying the acid radicals. Recourse 

 must be had to the Hinrichs system, page 420; or to separate carefully chosen identity tests. 



7. To a drop of a weakly acid solution add a fragment of metallic Mg. Note whether 

 the Mg becomes stained or coated with a crystalline deposit. To another drop add a frag- 

 ment of metallic Sn. See page 301. 



8. To a drop of a water or an acid solution of the substance add NH 4 OH by Method /, 

 page 299. Note whether a precipitate is produced and whether it is amorphous or crystal- 

 line. Test an amorphous precipitate by 9. Note whether precipitate is soluble in excess 

 of NH4OH; or if first formed slowly disappears. 



