256 



Scientific Froceedings, Royal Dublin Society. 



Iron. 



Ferric chloride gives a brilliant luminescence in the vacuum tube, both 

 with and without the condenser; but there is a difficulty in getting a 

 good photograph of the spectrum, as the capillary portion of the tube 

 is often rendered opaque by a black deposit that forms at an early stage 

 in the experiment : tliis is best guarded against by having only a small 

 quantity of the material present, and liaving it thoroughly dehydrated before 

 exhausting the tube. When a successful photograph is obtained, it contains 

 apparently all the lines of the spark spectrum of the metal, with much the 

 same relative intensities, so that there is no need to tabulate them in full, 

 but the following table gives the lines that are most prominent when only 

 a minute quantity of the substance is present, or only a short exposure 

 is given. The Leyden jar makes little difference other than to increase 

 the intensity of all the lines, or shorten the time of exposure necessary. N"o 

 prominent bands are seen. 



Principal Lines of Iron. 



