MICROCHEMICAL REACTIONS OF THE COMMON ELEMENTS 327 



Alkalies convert lead chloride into a basic chloride to which 

 the formula PbCl 2 3 PbO 4 H 2 O is generally assigned. 



Thallous salts yield with hydrochloric acid star- and cross-like 

 crystallites differing considerably from those given by lead. 

 There is little danger of confusing these two elements, since re- 

 crystallizing thallous chloride from hot water, in which it, like 

 lead chloride, is soluble, yields well-formed cubes. 



In the presence of chlorides of antimony and bismuth complex 

 chlorides of low solubility are sometimes formed, against which 

 the analyst should be on his guard. 



Silver gives an amorphous precipitate and mercurous salts a 

 fine granular one without resolvable structure. 



EXPERIMENTS. 



a. To a drop of a concentrated solution of Pb(NOa)2 add a drop of dilute 

 HC1 in the manner described above. Make several other preparations varying 

 the concentration of the test drops. 



b. Recrystallize a preparation of PbCl2 by heating to boiling with a large drop 

 of water. 



c. Recrystallize a preparation of PbCl 2 in the presence of NaCl, another in the 

 presence of KC1; of NRtCl; of CsCl. 



d. Test a solution of Pb and Sb. Then one of Pb and Bi. Then one contain- 

 ing all three elements. 



e. To a preparation of PbCl 2 add a drop of NH 4 OH. 



C. Through the Formation of a Triple Nitrite of Lead, Cop- 

 per and Potassium. 



To the moderately concentrated neutral test drop add a 

 trace of acetic acid, then a fragment or two of sodium acetate 

 and of copper acetate. Stir. Then add a fragment of potas- 

 sium nitrite. 



There is formed the salt K 2 CuPb(NO 2 )6 as tiny squares or 

 rectangular plates, or tiny cubes and rectangular prisms which 

 are brown by reflected light, jet black by transmitted light. The 

 crystals appear to be isometric. 



In this salt the potassium may be replaced by rubidium, yield- 

 ing a compound of lower solubility, or by cesium which will give 

 a salt of less and finally by thallium, one of least solubility and 

 therefore the test of highest delicacy. These salts are probably 



