2700 
XXIV. 
ON THE QUANTITATIVE SPECTRA OF MOLYBDENUM, 
TUNGSTEN, THORIUM, AND ZIRCONIUM. 
By A. G. G. LEONARD, A.B.C.S.L., 
Royal College of Science, Dublin. 
[Prare XXIV. ] 
[Read, Drecemper 17; Received for Publication, DrcEmMBER 29, 1907; Published, 
Fepruary 17, 1908. ] 
INTRODUCTION. 
Tue quantitative spark-spectra described in this paper have been 
investigated according to the method devised by Prof. W. N. 
Hartley,! certain modifications having been introduced in order to 
make the results readily comparable with previous work on the 
same subject.” 
The object of the work is to facilitate the use of the spectro- 
scope for analytical purposes by determining the lines which 
characterize the spark-spectra of the elements when present in 
solution in small quantities, as without a knowledge of these lines 
the elements present are not easily identified. 
The photographs were taken on a single prism quartz instru- 
ment made by Adam Hilger. The instrument when focussed 
for the less refrangible rays of the spectrum photographed from 
\ 5500 to A 2500. A Ruhmkorff’s coil, with a condenser and 
Hemsalech self-induction coil in circuit, was employed to obtain 
the spark. The plates were Cadett’s Royal Standard; and these 
were found to give excellent results with one minute’s exposure 
and subsequent development with hydroquinone. Gold electrodes 
1 Phil. Trans. Roy. Soc., vol. clxxy., 1884; Part 1., pp. 49-62; Part u., 
pp. 325-342. 
2 Proc. Roy. Dnblin Soc., vol. xi., 1907, pp. 184, 217, 229. 
