122 Dr. W. Marshall Watts on the Spectra 



carbon disulphide, turpentine, benzene, aniline, naphtha, 

 chloroform, ethylene dichloride, ethyl chloride, ethyl bro- 

 mide, and ethyl iodide; and in all cases observed the 

 " Swan" spectrum. 



Konen * also observed the spark in liquids, and obtained 

 the " Swan " spectrum with all carbon-containing liquids, 

 chloroform, benzene, carbon disulphide, carbon tetrachloride, 

 aniline, and petroleum. 



It would seem that the spark in a liquid containing carbon 

 and no oxy r gen offers the best chance of escaping oxygen- 

 contamination. We have then really a discharge in a small 

 gas-filled cavity of which the walls consist of the liquid 

 itself. 



Wilsingf, who also observed the discharge in liquids, 

 remarks, " One may hope in this way to obtain the percentage 

 of impurities greatly less than in Geissler tubes, which contain 

 only small quantities of the substance to be examined with 

 relatively large quantities of gases derived from the glass, 

 from the pump, or from the electrodes." 



Observations with the arc burning under liquids give the 

 same results, but the difficulties of excluding impurities are 

 greater than with the spark. 



Konen J observed the "Swan" spectrum from the arc 

 burning under alcohol, glycerine, carbon tetrachloride, 

 carbon disulphide, aniline, and petroleum, and also under 

 water if carbon rods were used. 



La Rosa § has observed the " Swan " spectrum in the 

 glow surrounding an intensely-heated carbon rod. The 

 image of the glowing rod (2 or 3 mm. in diameter) thrown 

 on the slit of the spectroscope gave an intense continuous 

 spectrum, and outside that a weaker and broader spectrum 

 on which are seen the " Swan''' 5 bands : y 5635 with four or 

 five edges ; S at 5165 with three or four edges : e at 4737 

 with four edges and three lines at 4383. On raising the 

 incandescence to the maximum 5165 was reversed. No 

 cyanogen lines are seen because the nitrogen of the air is 

 prevented from reaching the rod by the surrounding atmo- 

 sphere of carbon vapour. For the same reason oxygen 

 cannot reach the rod : therefore the spectrum is not due to 

 carbon plus oxygen, but to carbon vapour only. 



The experiment was repeated with the same result in a 

 space as free from oxygen as possible. 



* Konen, Ann. d. Thys. ix. p. 742 (1902). 

 + Wilaing, Szb. Berlin, 1899, pp. 426, 750. 

 J Konen, Ann. d. Pkt/s. ix. p. 742 (1902). 

 § La Rosa, Ann. d. Phys. xxxiv. p. 223 (1911). 



