ARC SPECTRUM OF ELECTROLYTIC IRON. 
997 
General Conclusions. 
In this paper I have given an account of the method employed in mapping the 
photographic spectrum of carefully prepared electrolytic iron. The region covered by 
the inquiry extends from \3900 to X6500, and the lines are compared with those 
mapped by Thalen, Kayser and Runge, and those which appear in McClean’s 
photographic maj^ of the iron spectrum. 
The comparisons have led to the following general conclusions :— 
(1.) Thalen’s work is, on the whole, strikingly confirmed, the visual spectrum as 
mapped by him differing but slightly in essential points from that which has been 
photographed at Kensington. 
The principal difference is in the greater number of lines mapped by Thalen in all 
regions except that between X4000 and X4300, and this is probably to be accounted for 
by the insufficient exposure of the photographs which was necessitated by the limited 
amount of material available for the experiments. 
(2.) The comparison with the spectrum photographed by McClean indicates 
that the experimental conditions employed by him produced a temperature not 
greatly differing from that of the arc employed at Kensington. There are only a few 
lines which are not common to the two series of photographs, and these in many 
cases can with great probability be ascribed to impurities present in one case and not 
in the other. Further, the apparent differences of intensity between some of the 
lines which are common, are mostly due to the superposition of the spectrum of air 
upon that of iron in McClean’s photographs. In some cases, however, there seems to 
be a real difference in the intensities of the lines, and this may, with much probability, 
be ascribed to the slight difference between the temperature employed at Kensington 
and that employed by McClean. 
(3.) The number of lines mapped by Messrs. Kayser and Runge is considerably 
in excess of that mapped at Kensington in corresponding regions of the spectrum. 
The comparison indicates that this is partly due to the fact that the iron employed in 
their experiments contained a greater number of impurities than that employed at 
Kensington. 
No origins have been traced for many of the lines present in their photographs 
which do not appear in the Kensington photographs, and some of these may therefore 
be really due to iron, their absence from the Kensington photographs being due to 
insufficient exposure or to the employment of a different temperature. The possible 
origins of 341 of these excess lines in Kayser and Runge’s list have been traced 
from the Kensington maps of metallic arc spectra. 
(4.) The impurities which contribute the greatest numbers of foreign lines to the 
spectrum are calcium and manganese. 
