ANALYTICAL CHEMISTRY
1792
CRYSTAL MORPHOLOGY Cry&al System. Orthorhombic. Form and Habit. Crystals from sodium acetate solution are usually elongated parallel to e with the prism 130 ) and macrodome { 201 I,, Occasionally the prism 110 1 also appears. Axial Ratio. a:b:e = 0.700:1:0.408. Intefiacial Angles (polar). 201 A 207 = 81' 10'. 130 A 730 = 500 56'. 110 A i i o = 690 56'. X-RAYDIFFRACTION DATA Space Group. Pc2,n or Pemn (f 1, Cell Dimensions. a = 11.41 A,; b = 16.31 A.; e = 6.66 A. a = 11.33.4,; b = 16.22A.; e = 6 . 6 6 A . ( 1 ) . Foymula Weights per Cell. 12 (12.07 calculated from x-ray
IIlead
Azide, Pb(N,),
(Form II)
crystals of lead azide, Form 11,. are . prepared by 6TWITABLE 4 . ~~~~. .. . .. . ~
slow diffusion ot lead and azide ions, usmg the apparatus shown in Figure 4. The pure water phase surrounding the two azide and lead nitrate solutions must he of added very carefully to avoid physical mixing of the two solut ions. The dish is covered and left undisturbed for several h,ours. If left for more than ahout 6 hours, some transformation tiD Form I may occur. Figures 5 and 6 show typical crystals of F'orm 11.
, ,
(L&C6,.
Formul a Weight. 291.3. Densit, r, 4.71 [displacement in benzene ( a ) ] , 4.68 (x-ray I.
Figure 4. Crystallization dish and small beakers arranged for formation of lead azide I1 by slow diffusion
:RYSTAL
MORPHOLOGT
Ullj.
Figure 3. Four successive photomicrographs during solution phase transformation of lead azide I1 (upper left) to lead azide I (lower r i g h t )
AxidRatio. a:b:e = 2.063:1:0.57'. Interfacial Angles (Polar). '011 A011 = 57" 38'. Profile Angle (Ohservedj. 59" 56'(projectionof 011 A 011 on
nn> 1vu,. Beta Angle.
107.5'
