1836.1 



29 



I now wish to call your attention to another peculiarity of the new 

 P.ontgen rays, that has just come to my notice, and had time permitted, I 

 should have had the specimens here to illustrate my remarks. 



The most exhaustive series of photographic experiments thus far made 

 in connection with the Rontgen rays are the investigations at the Im- 

 perial experimental institution at Vienna (K. K. Lehr- und Versuchs- 

 anstalt fur Photographic in Wien). Thus fiir no results have been 

 obtained greater than the original skeleton hand of Prof. Rontgen. Scien- 

 tifically, however, the curious fact has been learned that the actinic action 

 of the so-called X rays is dependent to a great extent upon the medium or 

 support that holds the haloid salts in suspension. 



It appears that for some reason as yet unknown the new Rontgen 

 rays have a peculiar affinity for a sensitive plate whose support consists 

 of animal matter or gelatine. Now if we take a plate of equal sensitive- 

 ness, but substitute collodion for gelatine, and expose it to the action of 

 the X rays, no effect whatever is produced. The rays seem to be abso- 

 lutely inert the moment any medium is substituted for the animal support 

 of the ordinary commercial drj'plate. 



This series of experiments at Vienna consisted in testing the ordinary 

 bromo-argentic gelatine dry plates of different degrees of sensitiveness 

 together with argentic-iodide collodion (wet) plates — bromide collodion 

 emulsion, and moist eosine bromo-collodion (Albert emulsion) and 

 argentic chloro-bromide collodion plates, the latter developed with an 

 alkaline solution. 



The result of this series of experiments was that the Rontgen rays made 

 little or no impression upon any variety of the collodion plates whether 

 wet or dry, while upon the contrary every variety of gelatine plate, no 

 matter whethersensitized with argentic bromide, iodide or chloride, proved 

 a ready recorder for the Rontgen rays. The most effective plates were 

 what are known in Germany as the " Schleusner Rapid " bromo-gelatine 

 dry plate ; they are equal in rapidity to our American plates " Sensomiter 

 23." 



It appears from this series of experiments that the most marked diflfer- 

 ence was found in the comparison of a chloro-bromo-gelatine dry plate 

 with a collodion wet plate, both of which were carefully tested as to their 

 equal sensitiveness by daylight prior to being exposed to the effect of the 

 X raj^s. Where the dry plate with alkaline development proved a suc- 

 cess, the wet plate with an acid-iron development was an absolute failure. 



Another peculiarity shown was that an alkaline development in every 

 case gave better results than a neutral or acid one. Then again when a 

 dry plate of the kind giving the best results was moistened or dampened 

 before exposure, the sensitiveness for the X rays was greatly diminished. 



Here perhaps we may find a solution to the problem why it is that none 

 of the American results obtained by use of the X rays thus far have been 

 equal, either in distinctness of outline or reproduction of detail, to the 

 German sciographs. It may be to the humidity of our atmosphere, more 



