

Fluorescence and Absorption Spectra of Sodium Vapour. o()o 



I fjreat deal of lioht on the mechanics of the sodium mole- 

 iile. and ^vill doiil)tless prove of considerable value in the 

 lopment of tlie theory of fluorescence. 



Apparatus Employed. 



The fluorescence as observed in exhausted glass bulbs is 

 never very intense, and the experiments can be continued 

 only for a few moments owing to the s})eedy corrosion of the 

 glass surface. Moreover, it is not possible to make use of 

 very dense vapour, the generation of which requires a high 

 temperature, owing to its action on glass. The form of tube 

 which was employed by one of us in a previous investigation 

 on the subject (Wood, Proceedinos of the Royal Soc. vol. Ixix. 

 p. 157 ; also Phil. Mag. Jan. 1902) enables vapour of great 

 density to be obtained, but owing to the rapid distillation to 

 colder parts of the tube the experiment cannot be continued 

 long enough for satisfactory photographic records. It is 

 important not only to have a very dense vapour but also to 

 have the vapour confined within a small region and sharply 

 bounded, in order that the light may not be weakened by 

 absorption before it reaches the denser portions. To meet 

 these requirements a new form of tube was designed and 

 constructed which gave admirable results. With it a fluores- 

 cence ten or fifteen times as bright as anything that can be 

 obtained with gla-ss bulbs was obtained and maintained con- 

 tinuously for five or six hours without recharging the tube. 

 This tube we have had in action for fully forty hours, and it 

 is only just beginning to show signs of leakage around the 

 l)razed joints, due to the action of the sodium at a red heat 

 on the silver with which the joints were brazed. The tube 

 can be very easily constructed, and when once charged can 

 be used over and over again without any preparation what- 

 ever for the exhibition of this most beautiful example of 

 fluorescence. Its general form is shown in Plate XIII. fig. 1, 

 The large tube was a piece of three-inch (16 gauge) Shelby 

 seamless steel tubing two feet in length. A ten-inch piece 

 of thin |-inch steel tubing was brazed with silver into the 

 large tube at the centre, making a right angle with it. 



Immediately below this tube and at a right angle to both 

 a small iron crucible was brazed into the larger tube, pro- 

 jecting into its interior to such a distance that its rim was 

 A-isible through the side tube. This crucible was made by 

 boring out a ^-inch iron cylinder. A small piece of brass 

 tubing was also brazed into the large tube near one end 

 through which the whole could be exhausted. The crucible 

 was filled with lumps of sodium, and the ends of the large 



