Behaviour of Metallic Vapours in Fl 



ames. 



29 



salt being brought in and out of the flame, and readings for 

 the pure flame and the streak of vapour made alternately at 

 each pressure. The flame was always adjusted as nearly as 

 possible to the same size; the brightness of the streak was 

 measured at each pressure by the pyrometer, and the 

 potential of the insulated electrode read. The luminosity 

 was kept approximately constant at all pressures by adjusting 

 the amount of salt on the wire ; the experiments at highest 

 pressure were done first, since, as mentioned, the salt does 

 not vaporize quite so readily here. 



Series of experiments over the range of pressures were 

 made with two different luminosities, i. e., rates of vapori- 

 zation. As already mentioned (§2), the deflexion of the 

 streak depends upon the rate of vaporization of the salt, 

 decreasing with decreasing rate, but reaching a constant 

 small value for amounts of salt below a certain limit. For 

 one series of experiments the rate was kept within this limit, 

 for the other a much greater constant rate was used, giving 

 a deflexion in the electric field three or four times as great. 

 The deflexion of the faint streak was not more than 5° 

 greater than that of the pure flame ; hence in some measure 

 it furnishes a check upon our estimate of the deflexion of 

 the pure flame at high pressure. It is found that whether 

 we subtract the deflexion of the faint streak, or the deflexion 

 of the pure flame estimated as described above from the 

 deflexion of the stronger streak, we have the same result : — 

 that with constant potential of the insulated electrode and 

 constant size of the flame the deflexion of the luminous 

 streak is approximately the same over the range of pressure 

 1 to 4 atmospheres. The following table exhibits this : — 



Table I. 

 Deflexion of the stronger streak. 



Pressure 



Flame angle 



Streak angle. 



Pyrometer 



a-9. 



(Atmospheres). 



9. 



a. 



(arb. units). 



4-05 



13° 



32° 



1-98 



19° 



39 



12° 



28° 



1-80 



16° 



39 



13° 



34° 



1-88 



21° 



3-8 



14° 



33° 



1-92 



19° 



3-15 



13° 



33° 



1-94 



20° 



2-55 



13° 



30° 



1-94 



17° 



1-9 



13° 



30° 



1-94 



17° 



1-3 



18° 



36° 



1-90 



18° 



10 



14° 



33° 



1-92 



19° 



