RADIOGRAPHY 



833 



between the two. Developing and fixing solutions made specifically for X-ray films 

 should always be used. The usual process of developing, fixing, and washing is fol- 

 lowed, but the times used are different. When the processing factors are correct 

 and the radiographs are found to lack density, it can be assumed that underexposure 

 has taken place, and when the radiographs are too dense, overexposure is indicated. 

 Any change in exposure time should be an increase or decrease of the original factor 

 by about 35 per cent. 



After a certain number of films have passed through the solutions, it will be found 

 necessary to add 1 min. to the development time to obtain the desired density. This 

 time, in turn, will have to be augmented by another minute at a later date. While 

 no formula can be given for change of development time* in general, after 100 films 

 14 by 17 in. have been processed, the development should be raised to 6 min. Smaller 



10 



0.4 0.6 031 



Hours 

 2 3 4 56810 152030406080100 200 400600 1,000 



2 3 4 567810 15 20 3040 

 Days 



Fig. 9. — Gamma-ray exposure chart for steel of various thickness. 



films take correspondingly less life from the solutions, and one 14- by 17-in. film can 

 safely be made to equal three 8- by 10-in. films, two 10 by 12 in., or one 11 by 14 in. 

 plus one 8 by 10 in. Likewise, after fifty 14- by 17-in. films, or equivalent, have been 

 processed, it is wise to increase the time to 7 min. At the end of another fifty units, 

 the solution has about reached the limit of its efficiency and introduction of new 

 solutions should be considered. The life of solutions varies so that the above recom- 

 mendation should be viewed more as a rough guide than as an absolute formula. 



In actual use the tank system, where proper temperature can be controlled by 

 regulating the flowing water around the tanks, is the most efficient system of process- 

 ing. Here the technique is merely to place the exposed film on a hanger which can be 

 conveniently immersed in developer, rinse water, fixer, and wash water for the pre- 

 determined intervals; the hanger should be held flat throughout the procedure. The 

 tray system may be used if a tank installation is not available, although more care 

 must be taken not to scratch or otherwise damage the surface of the film. 



