272 KEPOET— 1880. 



The vapour of frotobromide of iodine also gives an absorption spectrum 

 similar to the above (Gernez : ' C. R.' Ixxiv. p. 1190 — 1874). 



VIII. Fluorine. 



S^guin : ' C. R.' liv. p. 933 (1862). 



Salet : ' Ann. Chim. Phys.' xxviii. p. 34. (1873). 



A spark taken in fluoride of silicium shows a few lines, which are not 

 seen when the spark is taken in chloride of silicium. These lines Salet 

 attributes to the element fluorine ; they are all situated in the red. Seguin 

 observed a strong blue ray common to fluoride of silicium and fluoride of 

 boron, and attributes it to fluorine. Seguin does not say in what way the 

 gases were prepared, but it seems jjossible that the blue line is the calcium 

 line, which very often appears when calcium compounds are used in 

 preparing gases. 



IX. Sulphur. 



Seguin : ' C. R.' liii. p. 1272 (1861). 

 Mulder: 'Jour. f. Prakt. Chem.' xci. p. 112 (1864). 

 Pliicker and Hittorf : ' Phil. Trans.' civ. p. 13 (1865). 

 Salet : ' Ann. Chim. Phys.' xxviii. p. 37 (1873). 

 Lockyer: ' Proc. Roy. Soc' xxii. p. 374 (1875). 

 Gernez: ' C. R.' Ixxiv. p. 803 (1872). 



The Line-S2)ectrum. — If sulphur is heated to its point of ebullition in 

 a vacuum-tube, and the jar discharge passed through the vapour, we 

 obtain a line-spectrum, which was first measured by Pliicker and Hittorf 

 (Watts, Index of Spectra). Salet also has mapped this spectrum, and a 

 few of the lines have been measured by Angstrom (' Phil. Mag.' xlii. p. 397). 

 Seguin has obtained this spectrum by heating sulphur in hydrogen and 

 passing a spark at atmospheric pressure through the hydrogen. He was 

 thus the first to observe this spectrum. 



The Band-spedrum. — If the ordinary discharge is passed through a 

 vacuum-tube, in which sulphur is kept boiling, a beautiful band-spectrum 

 is obtained. Pliicker and Hittorf give a coloured drawing of this spec- 

 trum, but without measurements. Measurements have been supplied by 

 Salet, who furnishes us with the best investigation on sulphur spectra 

 which we at present possess. He was the first to observe this spectrum 

 as an absorption spectrum, by passing the light through sulphur vapour 

 heated to a high temperature, an observation which has been confirmed 

 by Gernez and Lockyer. 



The flame of sulphur, as weU as the flame of sulphuretted hydrogen, 

 gives a continuous spectrum only, but if a hydrogen flame contains traces 

 of sulphur a band- spectrum is seen. This spectrum was first obtained 

 by Mulder by heating sulphur near the orifice of a glass tube through 

 ■which hydrogen passed, the hydrogen being burnt at the orifice. Salet 

 increased the luminosity of the flame by pressing it against a layer of 

 cold water falling vertically. According to him the band-spectrum thus 

 obtained is the same as the one seen in a vacuum-tube ; the relative 

 intensity of some of the bands only being altered. Considering, how- 

 ever, the small dispersion used by Salet and the large differences between 

 the two spectra shown in his map, it seems probable that we have to deal, 

 in part, at any rate, with a new spectrum, most likely that of a compound. 



