Absorption of Rbntgens Bays by Solutions of Metallic Salts. 417 



deep. The middle cell 2 (above) is oblong in shape, being 137 mm. 

 long by 20 mm. wide. All the cells are made of paraffined mahogany 

 about 1*6 mm. thick. On the other side of the lead sheet the dark 

 slide containing the plate is placed, stops being arranged so that the 

 plate is always in the same position relatively to the wedges. 



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Fig. 2. 



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i 



1' 





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1 







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Opposite the cells three oblong holes 115 mm. long by 20 mm. wide 

 are cut in the lead sheet, so as to allow the rays to fall on the photo- 

 graphic plate ; the focus tube used was placed 300 mm. distant from the 

 plate, and was arranged so that the centre of the reflector or anti- 

 cathode was opposite the middle of the centre hole in the lead. 



In an experiment the two wedge-shaped cells 1 and 3 were filled 

 with the solutions that required testing, while the middle cell 2 was 

 filled with water. It was found that the intensity of the radiation 

 from the tube was very nearly constant over the whole plane of the 

 plate, the variation in intensity of the strip obtained opposite the 

 middle slit varying very little from one side to the other. Also, no 

 difference could be perceived when the cells 1 and 3 were filled with 

 the same 'liquid, thus showing that the variation in the vertical direc- 

 tion was negligible. 



In all experiments the same focus tube was used, the intensity of the 

 X rays being adjusted by heating. To give an idea of the penetrative 

 power of the rays used, it may be stated that at a distance of 12 inches 

 from the tube, the bones of the hand were clearly visible on a fluorescent 

 screen, while the flesh still appeared dark. By this very rough test 

 the tube was brought as nearly as possible to the same condition for 

 each experiment. It was found, however, that the use of different 

 penetrative powers had very little effect on the relative absorbing- 

 powers of the solutions, though the actual intensity of the rays was 

 greatly altered. In all experiments the plates used were Edwards' 

 " Cathodal Plates " (5 inches by 4 inches) ; they were developed by 

 hydrokinone and potassium carbonate in from ten to twelve minutes 

 during the warm weather, the time necessary being increased during the 

 colder months. 



