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XVI. 
INDEX OF THE PRINCIPAL LINES OF THE 
SPARK-SPECTRA OF THE HLEMENTS. 
By JAMES H. POLLOK, D.Sc. 
[Puates X. anp XI.] 
(Read, Decemper 18; Received for publication, DecrmBrr 21, 1906 ; Published, 
Juty 22, 1907.] 
Introduction. 
Tue following index of the principal lines of the spark-spectra of 
the elements is compiled to facilitate the use of spectrum photo- 
graphy in chemical analysis, by helping an observer to quickly 
identify groups of lines with which he is not already acquainted. 
For analytical purposes a complete list of all the possible lines of 
a particular element is not required ; what is wanted is a selection 
of those lines which are certain to develop under specific condi- 
tions, so that their presence or absence may be taken as proof of 
the presence or absence of the element in question. To supply 
this want I have selected from Watts’s “‘ Index of Spectra ”’} the 
principal lines of all the elements, and arranged them in order of 
their wave-lengths, with the symbol of the element and the 
intensity as given by Watts. Greek letters are added to indicate 
the quantitative spectra investigated by Professor W. N. Hartley,’ 
which are of the greatest importance. The quantitative spectra 
enable us to distinguish between the presence of a mere trace 
of an element and of a larger proportion, and even to deter- 
mine the quantitative composition ofa substance. Again, the 
absence of the residuary lines of an element conclusively proves 
the absence of that particular element, so that it is not necessary 
to consider other apparently coincident lines. Thus, if the alumi- 
nium lines 3092, 3082, and 2816, marked w, are absent, aluminium 
1 See also ‘‘ Introduction to the Study of Spectrum Analysis,’’ by W. Marshall 
Watts, 1904. 
2 Proc. Roy. Soc., 1882, p. 81; also Phil. Trans., 1884, Part 1., pp, 49-62; and 
Part 1., pp. 825-342. 
