MICROCHEMICAL REACTIONS OF LEAD 
369 
With simple mixtures, this test is a very beautiful one, but 
with complex material it is sometimes difficult to adjust the con¬ 
ditions, especially as regards the quantity of potassium thio¬ 
cyanate required. 
EXPERIMENTS. 
a. Test as above HgCl2, using Z11SO4. 
b. Try again, this time introducing a trace of CUSO4. 
c. Try this test with CUSO4 but with no ZnS04 present (which method is most 
satisfactory?). 
LEAD.i 
Crystal Forms and Optical Properties of Common Salts of Lead. 
A. ISOTPOPIC. —Nitrate (I). 
B. ANISOTPOPIC. 
Hexagonal. — Iodide. 
Tetragonal. 
Orthorhombic. — Bromide; chloridesulphate; tartrate. 
Monoclinic. —Acetate; chromate; thiocyanate. 
Triclinic. 
DETECTION. 
A. By Means of Potassium Iodide. 
Apply the reagent, by Method III, page 300, to the test 
drop slightly acidified with nitric acid. 
Lead iodide PbL is at once formed as a bright yellow precipi¬ 
tate in a circular band about the reagent fragment. The circle 
gradually becomes larger and larger and at its outside circum¬ 
ference beautiful hexagonal plates appear. These plates and 
flakes of lead iodide appear greenish or brownish yellow by 
transmitted light, sometimes even gray, according to their thick¬ 
ness. By reflected light lead iodide plates glow and glisten and 
display the iridescent colors of thin films, an extremely charac¬ 
teristic feature of this salt. 
These hexagons of lead iodide do not belong, according to 
^ Lead, silver and copper are introduced at this point rather than in their 
proper position in the Periodic System because of their close relations in qualita¬ 
tive analysis. 
* Recrystallized from hot water PbCfi is pseudohexagonal. 
