MICROCHEMICAL REACTIONS OF LEAD 375 



is added to increase the delicacy of the reaction a double chloride 

 of cesium and lead is formed which separates simultaneously 

 with or even before the triple nitrite. 



EXPERIMENTS. 



a. Test a preparation containing Pb. 



b. Try another preparation, this time introducing RbCl. 



c. Try again with CsCl. 



d. By a series of careful dilutions determine the limit of the precipitation of 

 Pb as the K salt, the Rb salt and the Cs salt. 



e. Test a mixture of Pb and Ni; Pb and Co; Pb and Ag. 



D. By Means of Metallic Zinc. 



Apply the fragment of metal to the center of the drop to 

 be tested; see Method 777, page 300. 



The characteristic appearance of the different metals when 

 separated from their solution by an element higher in the electro- 

 chemical series is often quite sufficient to enable the analyst to 

 identify it. The student is already familiar with these peculiari- 

 ties through the experiments performed as outlined on page 254. 



Lead yields beautiful long stiff many branching more or less 

 fern-like dendrites, whose side arms are usually at right angles 

 to the main stem or rib. Only portions of the formation show 

 bright metallic reflections. The chief characteristic of the "lead 

 tree" is a long fairly straight trunk or rib with side dendrites of 

 irregular length. 



Of "trees" formed by other metals that of silver most nearly 

 resembles that of lead, but is more delicate, more branching, with 

 side formations at angles other than 90 degrees and exhibits 

 splendid silvery white metallic reflections. 



Tin somewhat resembles silver but the side arms of the " trees" 

 are very oblique and parallel one with another, that is, the paral- 

 lelism extends across the main axis or rib. The reduction is 

 slower with tin. 



None of the remaining metals yield long loose fern-like or tree- 

 like forms. Bismuth gives black and gray feathery and mossy 

 dendrites with sharp-pointed ends with a characteristic curving 

 tendency of the ends of the clusters. The mossy dendrites appear 



