﻿Electricity in Flames containing Metallic Vapours. 875 



The insulated screen of thin platinum foil, pierced with a 

 rectangular horizontal slit (3 mm.xl2 mm.), was brought 

 into the flame between the bead and the earthed electrode, 

 and arranged in different experiments with the slit at various 

 heights above the bead. Curves of the type shown in fig. 4 



Fig:. 4. 



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2 

 Current . 



were obtained in all cases ; the maxima are sharp considering 

 the breadth of the slit. (These curves are taken at random 

 as typical ; they are not all three made with the same bead.) 

 This indicates that the carriers have all approximately the 

 same velocity ; the fact that curves made at different heights 

 with the same streak of vapour give all about the same 

 maximum deflexion indicates again that the carriers proceed 

 only from the edge of the luminous streak, for the streak 

 increases in breadth as we go upwards. The very flat 

 maxima in the curves obtained for the unscreened streak 

 offer additional confirmation of this point. (See fig. 1.) 



The effect of increasing the air-gap between the flame and 

 the earthed electrode was examined. It was found to 

 diminish markedly the metallic current for all positions of 

 the platinum strip. An example of the effect is shown in 

 fig. 6 ; the solid and dotted curves on the right of the figure 

 represent respectively the metallic current obtained with an 

 air-gap of 8 mm. and 18 mm. respectively. The same figure 

 exhibits the effect for negative carriers to be referred to 

 later. This shows that a certain number of the carriers 

 become permanently neutralized, and pass upwards. 



§ 7. The Faster Carriers are Metallic. 

 It was observed that if the platinum strip was carefully 

 cleansed in the Bunsen flame before beino- used to detect the 



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carriers, yet it afterwards gave the sodium colour in the 



