Nov. 17, 1887] 



NATURE 



57 



In bunscn — 

 Mg 

 Ma 



Flutings 



5000 



5580, 5860, 6145, 5340 



Seen on passing from the temperature of the 

 btmsen to that of the oxy-coal-gas flame — 



Ba 6010, 6350, 6480 



Cr 5360, 5570, 5800, 6040 



Fe 6150 



Cu 6050, 6130 



Zn 5460, 5680, 4985, 5140, 5340 



All the (lutings, with the exception of magnesium, have their 

 maxima towards the blue, and shade off towards the red end of 

 the spectrum. (See Map i.) 



C. Experiments upon Mg at low temperatures. 



I have a rain gone over the experiments already communicated 

 to the Royal Society (Proceedings, vol. xxx. p. 27), and in 

 addition have observed the spectrum of the metal burning in the 

 centre of a large bunsen burner, in which case we get the line at 



5201, and the fluting in the position of b without the fluting at 

 500. In the Bunsen as ordinarily employed the fluting at 500 

 far eclipses the other parts of the spectrum in brilliancy, and at 

 this temperature, as already observed by Messrs. Liveing and 

 Dewar (Proc. R.S. vol. xxxii. p. 202), the ultra-violet line 

 visible is that at 373. I,ecoq de Boisbaudran has observed 

 the lines in the chloride at 4705 and 4483 (" Spectres Lumi- 

 neux," p. 85). 



D. Experiments upon the glow of Na and Mg in vacuum 

 tubes. 



A small p'ece of sodium, free from hydrocarbon, was placed 

 in the lower limb of an end-on spectrum tube, and arrangements 

 made for ob erving the spectrum of the gas evolved when the 

 sodium was heated. Having first obtained as perfect a vacuum 

 as possible, the sodium was gently heated, sMid the spectrum of 

 the gas then gave nothing but the C and Y lines of hydrogen. 

 The pump being stopped and the sodium heated, a point was 

 reached when C and K became very dim and were replaced by 

 the structural spectrum of hydrogen. 



Map t. — Spectra of mjtals at the temperature of the o.'cy -coal-gas blowpipe. 



In another experiment the sodium was replaced by a piece of 

 magnesium along the end-on tube. The same proce-s being 

 gone through, similar phenomena were observed, but in the 

 latter case there was a line at 500, in addition to the lines seen 

 in the case of sodium. 



The important point, then, is the existence of a line at 500 

 in the spectrum when magnesium is heated, and the absence of 

 such a lins in the gas evolved from sodium under the conditions 

 stated. 



E. Experimen's upon the conditions under which the C and 

 F lines of hydrogen disappear from the spectrum. 



The association of the bright lines of hydrogen with nebuli?e 

 and many of the stars with bright lines and the so-called new 

 stars points out at once that it is important to consider the 

 various changes which hydrogen can undergo under various 

 conditions of temperature and pressure. I pointed out many 

 years ago that, when under certain conditions the spectrum of 

 hydrogen is examined at the lowest possible temperature, the F 

 line retains its brilliancy long after C disappears ; and the fact 



that, after all the lines of hydrogen may be made to disappear 

 from the spectral tube, the spectrum which remains visible, and 

 is sometimes very brightly visible, is a'so due to hydrogen, has 

 always been a matter of thorough belief in my mind, although 

 so many observers, down even to M. Cornu not so very 

 long ago, have been inclined to attribute it to the existence of 

 " impurities." 



I began to map the so-called structural spectrum at the College 

 of Chemistry in 1869, but other matters supervened which pre- 

 vented the accomplishment of this work. This, however, is a 

 matter of small importance, because quite recently Dr. Hasselberg 

 has communicated to the St. Petersburg Academy an admirable 

 memoir on the subject, accompanied by a map (Memoires de 

 I'Academie Imperiale, series vii. vol. xxx. No. 7, Hasselberg). 

 The brightest portions of the structure spectrum are shown in 

 Map 2. 



The most convenient way of obtaining a supply of hydrogen 

 for investigations of this kind i- to use a little sodium which has 

 never been in contact with hydrocarbon, or a piece of magnesium 

 wire ; to place them in the low end of a glass tube, one part of 



