X-RA VS AND ORIEXTA TlOX OF QUARTZ CRYSTALS 335 



of the liead can ho adjusted through small angles and clamped in the ad- 

 justed position. The jig is then placed in an X-ray goniometer set for 

 reflection from the phine to be used and the slab adjusted until maximum 

 reflection is obtained. The jig itself is not moved. If the slab were per- 

 fectly cut the maximum reflection would be obtained when the head of the 

 jig was normal to the jig axis. A miscut will give maximum reflection at 

 some other angle and, when clamped at this angle of maximum reflection, 



Fig. 3.29 — Orientation of AT and BT plates and slabs with respect to Z section {-\-X to- 

 ward reader for right-handed quartz) 



will have a surface ground on it normal to the axis of the jig. This surface 

 will have the desired orientation of the plate. 



As in the case of the finished plate the slab must be checked for angle- 

 error around two mutually perpendicular axes in the plate surface. The 

 intersection of the slab surface with the Z-cut surface is commonly taken 

 as one axis and the normal to this as the other. 



For the AT and BT cuts these two axes are the same ones used in cor- 

 recting the finished plate and the same settings for jig holder and ionization 

 chamber may be used (See Fig. 3.29). For any cut with an A3 angle that 



