MoKROW — Spectra of Manganese, Lead, Copper, and Lithium. 275 



give almost a complete spectrum in a vacuum-tube. In No. II are seen 

 many lines which appear when even still less than "0001 gramme of the 

 metal is used, and No. Ill shows the ultimate lines of manganese, 

 appearing wlien the most minute trace of the element is present. Tliese 

 ultimate lines did not appear at all on the photograph of the spectrum taken 

 when the tube had been boiled for a second time with hydrochloric acid. 



When the spectrum was being photographed for the second and third 

 time, the colour in the tube was rose, the green luminescence seen before 

 having disappeared. Lines due to chlorine appear in all the photographs. 



A very characteristic group of three lines, X 2801*3, A 2798-5, and 

 A 2795"3, which are due to manganese appear in Dr. Pollok's vacuum-tube 

 spectra' of manganese, potassium chloride, barium chloride, and metallic 

 lithium, and as they are not the ultimate lines of the spark-spectrum of 

 manganese, and no other lines of manganese appear, their presence seemed 

 peculiar. They may be seen on Dr. Adeney's photograph of the grating 

 spectrum of manganese,^ but are not nearly so strong or characteristic as 

 in the vacuum-tube spectra. From my photographs it is evident that as 

 these three lines are strongest on the last photograph of manganese, tiiey are 

 the ultimate lines of the vacuum-tube spectrum of that substance, and are 

 quite different from tlie ultimate lines given by the spark-spectrum, which 

 are X 2605-8, X 2593-8, and X 2576-2. 



The characteristic group of tliree lines referred to above are thus accounted 

 for as being due to tlie merest trace of manganese. 



' Scient. Proc. Eoy. Dub. Soc., 1912, vol. xiii., p. 233. 



' Trans, Koy. Dub, See, Ser. ii, 1901, vol. vii, Plate XXVII. 



