ON OUR KNOWLEDGE OF SPECTRUM ANALYSIS. 273 



Some of the bands of the electric spectram no doubt may be present as 

 well. 



The Goniinuous Spectrum of Sul^liur. — Sulphur vapour at compara- 

 tively low tempei'atures shows a continuous spectrum by absorption. 

 The change of this continuous spectrum to the band-spectrum seems to 

 be connected with and dependent on the change in density which sulphur 

 vapour undergoes between the temperatures of 500° and 1000°. Gernez 

 at least mentions that the change takes place simultaneously with a rapid 

 decrease in density. 



X. Selenium. 



Mulder: 'Journ. f. Prakfc. Chemie,' xcL p. 113 (1864). 

 Pliicker and Hittorf : ' Phil. Trans.' civ. p. 5 (1865). 

 Salet : ' Ann. Chim. Phys.' xxviii. p. 47 (187.3). 

 Gernez : ' C. R.' Ixxiv. p. 803 and p. 1190 (1874). 

 Lockyer and Roberts : ' Proc. Roy. Soc' xxiii. p. 348 (1876). 



The spectra of selenium are analogous to those of sulphur, and are 

 obtained in the same way. Accoi'ding to Salet the band- spectrum may 

 be obtained in the flame of burning selenium, or when the metalloid is 

 heated in a hydrogen flame (Mulder). Sulphur, as we have observed, 

 gives under the same conditions a continuous spectrum only. The band- 

 spectrum of selenium has been obtained by absorption in selenium vapour 

 by Gernez. At 700°, according to this observer, the vapour of selenium 

 absorbs all the light with the exception of the red ; but if the temperature 

 is raised the tint of the vapour brightens, and the different I'egions of the 

 spectrum re-appear, furrowed with groups of black bands in the blue 

 and violet. The band-spectrum has also been obtained by Lockyer as an 

 absorption spectrum. 



Gernez also describes the absorption spectra shown by the vapours of 

 selenious acid, protochloride of selenium, and bromide of selenium ; but 

 he does not give any measurements. 



XI, Tellurium. 



Thalen: 'Nov. Act. Ups.' (Ill) vi. (1868). 

 Salet: ' Ann. Chim. Phys.' xxviii. p. 49 (1872). 

 Gernez : ' C. R.' Ixxiv. p. 1190 (1872). 



The Une-spedrum of tellurium can be obtained, like that of metals, by 

 taking the jar discharge from tellurium poles in air. It has been mea- 

 sured by Thalen. Salet has observed a band-spectrum in vacuum-tubes 

 in which tellurium was heated, but he could not decide whether this 

 spectrum did not rather belong to an oxide. Gernez heated tellurium in 

 an atmosphere of carbonic acid gas to a temperature near that at which 

 glass begins to melt, and he observed in the transmitted light an absorp- 

 tion spectrum, extending from the yellow into the violet. 



Protochloride of tellurium, according to the same observer, gives a band- 

 absorption spectrum, chiefly in the orange and green. The vapour of 

 protobromide of tellurium absorbs the light in the red and yellow. 



XII. Phosphorus. 

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

 Pliicker and Hittorf : ' Phil. Trans.' civ. p. 24 (1865). 

 Salet: 'Ann. Chim. Phys.' xxviii. p. 56 (1873). 

 1880. T 



