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LIV. On the Spectra of some Gases under High Pressures. 

 By M. A. Wiillner*. 



A PAPER by M. Wiillner has already appeared in this 

 Journal f on the various shapes which the spectrum of a 

 gas traversed by an electric spark is capable of assuming* when 

 the pressure of the gas or the temperature produced by the 

 passage of the spark is varied. In his first research M. Wiillner 

 had only worked with hydrogen, oxygen, and nitrogen under 

 low pressures ; but he has subsequently resumed this investiga- 

 tion with the aid of M. Bettendorff ; and the use of a far more 

 powerful induction-coil has enabled him to examine how the 

 spectrum of the electrical discharge is affected when, instead of 

 a rarefied gas, it traverses a gas under a more or less high 

 pressure. 



Apparatus. 



The apparatus used was arranged so that the pressure inside 

 the spectrum-tube could be easily varied from an almost perfect 

 vacuum up to two or three atmospheres. For this purpose it 

 consisted essentially of a large U-tube with legs of unequal length. 

 The longer was at least 2*5 metres long and was open at the 

 top ; it contained the mercurial column which measured and ap- 

 plied the pressure. In the bend of the U-tube was a glass cock 

 by which the mercury of the tube could be allowed to flow out. 

 The Geissler's tubes used had essentially the same construction 

 as those previously used ; they were provided with two adjutages, 

 each of which had a glass stopcock. 



The shorter leg of the U-tube extended about 770 millims. 

 from the bend; and to it was fused one end of the Geissler's 

 tube. The lower adjutage was connected, through a Liebig's ap- 

 paratus containing concentrated sulphuric acid and a tube con- 

 taining anhydrous phosphoric acid, with the gasometer. The upper 

 adjutage was connected with aGeissler's air-pump provided with 

 drying-arrangements containing phosphoric acid. The spectrum- 

 tube was of the ordinary shape — that is to say, a very short ca- 

 pillary tube connecting two larger ones. It had two pairs of elec- 

 trodes, one with a distance of 8 centims. ; the others ended just 

 at the extremities of the capillary part of the tube, and were about 

 16 millims. from each other. 



In making the experiment, it was first of all necessary to fill 

 the apparatus with perfectly pure and dry gas. After having 

 introduced into the U-tube a quantity of mercury enough 



* Translated from an abstract in the Bibliotheque Universelle de Geneve 

 for September 1869, of the original in Poggendorff's Annalen,\o\. exxxvii. 

 p. 337. 



f Phil. Mag. S. 4. vol. xxxvii. p. 405. 



