372 
ELEMENTARY CHEMICAL MICROSCOPY 
Lead chloride PbCh separates at once in the form of char¬ 
acteristic, white, long acicular crystallites belonging to the ortho¬ 
rhombic system. There are also seen feathery dendritic X’s and 
long irregular ragged prisms. 
The appearance of the lead chloride separating varies with the 
concentration of the solution being tested and with the nature 
of the substances present. If the test drop is not sufficiently 
concentrated the lead chloride will not separate at once in the 
form of the characteristic crystallites, but will appear more 
slowly, prismatic forms being the rule. This question of con¬ 
centration becomes a most important one if the substance con¬ 
tains salts with which lead chloride can unite to form double 
salts, as for example chlorides of the alkali metals and ammonium, 
for in such an event dilute or even moderately concentrated 
drops fail to yield recognizable forms. Indeed it may be said 
that testing for lead with hydrochloric acid is not advisable in 
the presence of members of Groups I and II. 
In neutral solutions of lead acetate there may be precipi¬ 
tated in the presence of members of Group I and no excess of 
the reagent, colorless, highly refractive prisms of the formula 
Pb(OH)Cl {n = 2.08 to 2.16) belonging to the orthorhombic sys¬ 
tem but sometimes also appearing as monoclinic prisms. 
Lead chloride is slightly more soluble in water containing a 
little nitric acid than in pure water, hence the separation of lead 
as chloride is never complete. 
Lead chloride differs from the chlorides of silver and mercurous 
mercury in being easily soluble in hot water, thus affording a 
simple method of separation. On cooling, the lead chloride no 
longer appears in the forms stated above but assumes that of 
thin pseudohexagonal prisms, rhombs and hexagons. 
Recrystallized in the presence of Group I, double chlorides 
result, which generally separate more slowly. The crystal form is 
quite different from that of the normal salt. It is quite impor¬ 
tant that the student should be familiar with at least the double 
chloride of cesium and lead (cesium chloroplumbate), since this 
compound not infrequently makes its appearance when testing for 
tin with cesium chloride and is quite apt to puzzle the beginner. 
