MICROCHEMICAL REACTIONS OF CHROMIUM 403 



A great excess of hydrochloric acid seriously reduces the 

 delicacy of the reaction, while nitric and sulphuric usually pre- 

 vent the separation of typical crystals. 



The student must bear in mind the caution given under anti- 

 mony that cesium chloride has a strong tendency to form double 

 salts, especially with lead, copper, cadmium, zinc, aluminum, etc. 



EXPERIMENTS. 



a. Try CsCl upon a solution of Sn in HC1. 



b. Try the test upon Sb in HC1 solution; upon Bi in HC1 solution. 



c. Try converting the chloro-salts of these three elements into the iodo com- 

 pounds. 



d. Try testing for Sb and Bi in turn in the presence of a little Cu. 



e. Try mixtures in which some of the other metals are present which form 

 crystallizable double chlorides with CsCl. 



D. Other Important Tests. 



With Primary Potassium Oxalate. (See Manganese, Method 

 A, page 406.) 



With A mmonium Bichromate. (See Silver, Method B, p. 380.) 



CHROMIUM. 



Crystal Forms and Optical Properties of Common Salts 

 of Chromium. 



A. ISOTROPIC. Chrome alums (I). 



B. ANISOTROPIC. 



Hexagonal. 



Tetragonal. 



Orthorhombic. Barium chromate (or M) ; calcium 

 chromate (or M); potassium chromate; sil- 

 ver chromate; sodium chromate; strontium 

 chromate (or M); zinc chromate. 1 



Monoclinic. Ammonium bichromate ; ammonium 

 chromate ; barium chromate (or O) ; calcium 

 chromate (or O) ; lead chromate ; strontium 

 chromate (or O). 



Triclinic. Potassium bichromate; silver bichro- 

 mate; 2 sodium bichromate. 



1 Iri the presence of FeSO4 7 H 2 O the salt separates monoclinic. 



2 Ag 2 Cr 2 O 7 dissolved in water decomposes into Ag 2 CrO 4 and CrO 8 . 



