Chemistry and Physics. 197 



more, the maximum of fluorescence should shift toward the red 

 as the atomic weight increases. 



These expectations have been realized by the recent work of 

 Steubing. The details of the apparatus used will not be dis- 

 cussed in this place ; suffice it to say that the elements were 

 vaporized in specially designed quartz vessels which were heated 

 by means of either a Bunsen flame or a helix of wire carrying an 

 electric current. For sulphur the exciting light was derived from 

 an iron arc of about 5 amperes and 220 volts, while for selenium 

 and tellurium an ordinary carbon arc sufficed. For selenium, and 

 especially for sulphur, it was necessary to have the element in as 

 pure a condition as possible, and hence great care had to be taken 

 to exclude foreign gases from the quartz cylinders. On the other 

 hand, the fluorescence of tellurium vapor was not very sensitive 

 to the presence of impurities. The most important remaining 

 facts discovered by Steubing may be summarized in the following 

 words : (1) The four elements of the sixth column of the periodic 

 system exhibit fluorescence in the vapor state. (2) As the atomic 

 weight increases the fluorescence spectrum as a whole is displaced 

 from the shorter towards the longer region of wave-lengths. (3) 

 The region of excitation lies, («) for oxygen, below 2000 A. XL, 

 (b) for sulphur, between 2500 and 3200 A. IT., (c) for selenium, 

 above 3000 A. XL, and extends into the visible spectrum, (d) for 

 tellurium, in the more refrangible part of the visible region. (4) 

 In order to obtain fluorescence it is necessary for the vapor to have 

 a definite density and a definite temperature. This is especially 

 true in the case of sulphur, for which the vapor must be super- 

 heated between 400° C. to 500° C. (5) The fluorescence spectra 

 are discontinuous and consist of more or less " washed-out " 

 groups of lines which appear to be bands. — Physik. Zeitschr., 

 No. 18, p. 887, Sept., 1913. h. s. u. 



8. The Series Lines of Neon.- — In the year 1911 Watson pub- 

 lished an account of his unsuccessful attempt to discover line 

 series in the spectrum of neon. He only found, among the 

 relatively strong lines, several groups which repeated them- 

 selves with constant frequency difference. Recently R. Rossi 

 has subjected Watson's wave-lengths to careful scrutiny and dis- 

 covered three series among the faint lines. Two of the series lie 

 entirely in the visible spectrum and are composed of doublets 

 with constant frequency difference (167'5) between the members 

 of the pairs. Since these two series also converge towards the 

 same limit, 411 9"8 A.U., they resemble subordinate series. Never- 

 theless all efforts to find the associated principal series have failed. 

 Furthermore, the neon series do not correspond to any of the 

 subordinate series of helium, for, although the neon series are 

 nearer to the red end of the spectrum than the helium series, as 

 would be expected, the approximate relation between the sepa- 

 ration of the doublets and the square of the atomic weight is not 

 fulfilled. Rossi uses Rydberg's formula because the number of 

 lines found for each series is small, namely, seven doublets in the 



