SURFACE LAYERS OF CRYSTALS 



139 



photographic films or plates in addition to the ionization chamber for meas- 

 uring the reflected rays. 



2.2 Reflection- Intensity Measurements on the Single Crystal 

 Spectrometer with the Ioniz.vtion Chamber (Fig. 2) 



Working with the single-crystal spectrometer, Bragg, James and Bosan- 

 quet* found the reflection-intensity from a ground face of rock salt two to 

 four times that from a cleavage face. Dickinson and Goodhue* found the 

 reflection-intensity from ground faces of sodium chlorate and sodium 



COLLIMA 

 SLI 



IONIZATION 

 CHAMBER 



Fig. 2. — Single crj'stal spectrometer 



bromate twice that from the natural face. Sakisaka' found the reflection- 

 intensity from a quartz plate lapped with ^30 carborundum 2:} times 

 that from a plate lapped with very fine emery, which, in turn, was twice that 

 from an etched plate. Recent measurements by the writer have shown that 

 the reflection-intensity of an etched surface increases with progressive lap- 

 ping and that of a ground surface decreases with progressive etching as shown 

 in Fig. 3. In these figures the reflection-intensity is given in terms of the 

 ratio of the intensity from the test plate to that from a standard plate of the 

 same cut, etched 20 minutes following fine lapping. The initial rate of in- 

 crease of intensity- ratio with lapping or decrease with etching is very high. 



This technique would be most useful in sample-testing groups of plates to 

 check whether they had been inadequately etched or whether any lapping at 

 all had occurred after etching. (In either case the plate would be subject to 



^ Bragg, W. L.; James, R. W. and Bosanquet, C. H.; "The Intensity of Reflexion of 

 X-Ravs by Rock Salt," Part I. Phil. Ma^. 41 (1921) pp. 309-337; Part 11, Phil. Mas. 42 

 (1921) pp. 1-17. 



"'Dickinson, R. G. and Goodhue, E. A.; "The Crystal Structure of Sodium Chlorate 

 and Sodium Bromate," Joi<r. Amer. Chem. Soc. 43 (1921) pp. 2045-2055. 



' Sakisaka, Y.; "The Effects of the Surface Conditions on the Intensity of Reflexion of 

 X-Rays by Quartz," Japanese .Tour. Phvs. 4 (1927) pp. 171-181. 



