MICROCHEMICAL REACTIONS OF COPPER 385 



elements analogous to arsenic as shown by their position in 

 the Periodic System. We find, for example, crystalline salts 

 of silver with phosphorus, as silver phosphate; with antimony, 

 silver antimonate; with vanadium, silver vanadates; with chro- 

 mium, silver chromates; with molybdenum, silver molybdates. 

 Of these salts the chromates and vanadates can be employed for 

 the detection of silver, but the phosphates, antimonates and 

 molybdates cannot be made to yield sufficiently characteristic 

 results. 



EXPERIMENTS. 



a. Test a neutral solution of AgNO 3 in the manner suggested above. 



b. Recrystallize a preparation of Ag 3 AsO 4 from HNO 3 . 



c. Try another preparation with NH^OH. 



d. Test a mixture of Ag and Pb. Then one of Ag and Hg. 



e. Try the above reaction on salts of Ca, Sr and Ba, first alone, then in mix- 

 tures but with no Ag present. 



/. Try salts of Mg, Zn and Cd. 



g. Try a salt of Ca in the presence of much NI^Cl. 



COPPER. 



Crystal Forms and Optical Properties of Common Salts of 

 Copper. 



A. ISOTROPIC. Cuprous chloride, bromide and 



iodide. 



B. ANISOTROPIC. 



Hexagonal. 



Tetragonal. Ammonium-copper chloride; potas- 

 sium-copper chloride. 



Orthorhombic. Chloride; sulphate plus 4 NH 3 . 



Monodinic. Acetate; potassium-copper sul- 

 phate. 



Triclinic. Sulphate. 



DETECTION. 



A . By Means of Potassium Mercuric Thiocyanate. 



The reagent is applied by Method /, page 299, to neutral or 



weakly acid solutions ; it must be neither alkaline nor ammoniacal. 



The appearance, properties and peculiarities of copper mercuric 



