Sensitiveness of FhotograpJiic Plates to X-rays. 42-3^ 



Each plate was exposed in from five to eight strips, the exposures 

 of successive strips increasing in a constant ratio. Tliere was also^ 

 a fog-strip which was shielded from radiation the whole time. 



Ihe distance from plate to anticathode was 100 cms. The cur- 

 rents used varied from .03 to .06 milliamijere. The pressures 

 used were 31.5, 73.0, 83.0 kilovolts corresponding to spark-gaps^ 

 of 1.5, 5.0, 7.0 cms., respectively between spheres of 6.5 cms. 

 diameter, the cathode being earthed. ^ The minimum wave-lengths' of 

 the radiation were, therefore, .390x10-8, .173x10-8, and .152x10-8 

 cms. respectively. 2 The wave-lengths of the K and L characteristic 

 radiation for silver are .56 x 10*8 and 4.17 x 10-8 cms., and for 

 bromine 1.05 x 10-8 and 8.48 x 10-8 cms. 



The developer was one often used in radiography, as follows^ : — 



Solution A. 



Hydroquinone 25 gms. 



Potassium metabisulphite 25 gms. 



Potassium bromide 25 gms. 



Water 1000 c.c. 



Solution B. 



Potassium hydroxide 50 gms. 



Water ... ; 1000 c.c. 



llie two solutions were mixed in equal proportions immediately 

 before use, and the plates were developed at a temperature of 

 20"^ C. for 4 minutes. After 4 minutes' development the density 

 due to the exposure had reached its maximum value and further 

 development only increased the fog-density of the whole plate. In 

 order to verify this an Ilford X-ray plate was cut into three pieces, 

 which were exposed simultaneously. On each piece there was a 

 strip which received an exposure of 8.7 x 10>5, one which received' 

 4.1 X 10^ volt. 2 amp. sec. cm-2, and an unexposed or fog strip. The- 

 three plates were then developed at 20° C. for periods of 3, 4, and' 

 5 minutes respectively. The lesulting densities are tabulated 

 below under D^ and D.^, which are the densities due to the ex- 

 posures given, the fog-density, "Df, having been subtracted from- 

 the measured densitv. 



1 F. W. Peek. "Dielectric Phenomena in Hijfh Voltaj,^* Engineerinp," p. 89. 



2 Hull. Phys. Rev., vii.. 1916, p. 156. 



3 Sahni. Phil. Maj., xxix., 1915, p. 836. 



