Adeney — Photographs of Spark Spectra from the Rondand Spectrometer. 335 



of air may be, the lines and bands of oxygen and nitrogen do not obscure or 

 suppress those of the elements which constitute the electrodes. The stream of 

 vapour of greater density than air fills up the track of the spark and excludes the 

 gases of the atmosphere. 



In such cases the electrodes give an imperfect air spectrum, and such imper- 

 fections are characteristic of certain metals. In measuring air lines some of the 

 metals were found to be more suitable than others. Metallic lines also suppress 

 neighbouring air lines, and owing to their greater emissive jjower are easily 

 distinguished. 



Experimental Details. 



The pi'esent series of spectra form a continuation of the work above quoted. 

 They have been photographed from the Rowland's concave grating, which has 

 recently been mounted in the Royal University, Dublin. The grating has a focal 

 length of 21 "5 feet, and a ruled space of six inches, with 14,438 lines to the 

 inch. 



The mounting of the spectrometer in the Royal University has already been 

 described by the author, in conjunction with Mr. J. Carson, a.r.csc.i., in the 

 Scientific Proceedings of the Royal Dublin Society, 1898.* 



A current of ten amperes, and a ten-inch coil by Apps, were employed, with 

 a condenser 144 square inches in area, for " sjiarking." 



The specimens of the metals used as electrodes were, it is believed, of a high 

 degree of purity. 



The specimen of iron was prepared from pure crystallized potassium ferro- 

 cyanide in the same manner as that employed in the investigation by Hartley 

 of the ox5'hydrogen flame spectraf ; also of the arc spectra by Hartley and 

 Ramage, for comparison with the solar sjDectrum when measuring the lines of 

 gallium. :j: 



The specimens of cobalt and nickel were portions of those prepared by 

 Dr. W. J. Russell, f.r.s., in his researches upon the atomic weights of those 

 metals. 



Specimens of ruthenium, rhodium, palladium, osmium, iridium, and platinum 

 were very kindly presented by Messrs. Matthey and Johnson for the purpose of 

 this research. 



The chromium spectrum was obtained by sparking a saturated solution of 

 potassium chromate between platinum electrodes. 



*See also Phil. Mag., vol. xlvi., p. 223, 1898. 



tPMl. Trans., vol. clxxxv., p. 161, 1894. 



X Sci. Trans. Eoy. Dublin Soc, vol. vii., ser. 2, 1898. 



