250 Mr M c Glelland, On the Conductivity of Gases 



carriers in the two gases are not made in exactly similar 

 conditions. 



The arc in C0 2 . 



(12) When the arc is formed in C0 2 there is an important 

 difference in the conductivity of the gas drawn from it compared 

 with that in air or oxygen ; a negative charge is discharged by 

 the gas much more rapidly than a positive charge. The discharge 

 is still brought about in the same way as in the previous cases ; 

 the current varies with the E.m.f. in the same manner, and the 

 conductivity of the gas can be entirely destroyed by passing 

 it between two terminals kept at a sufficiently great difference 

 of potential. Since the conducting gas discharges negative elec- 

 tricity more readily than positive, the positive carriers are there- 

 fore present in greater number than the negative. We had a 

 similar result in air and oxygen, but there the excess of positive 

 was small, whereas in C0 2 the amount of positive is often many 

 times that of the negative. In one experiment when the ter- 

 minal B (Fig. 1) was charged negatively its rate of leak was 



100 scale divisions in 15"; 



when charged positively it was only 



10 scale divisions in 60". 



The negative carriers therefore do not come away from the arc 

 in anything approaching the same amount as the positive. 



(13) The small excess of positive electricity in the gas from 

 the arc when air or oxygen is used was explained above by the 

 greater loss of negative carriers to the terminals on account of their 

 greater velocity under electric force. 



If this explanation can account for the great excess of positive 

 in the case of C0 2 we must assume that in the arc itself the velocity 

 of the negative carrier is great. We know as mentioned above 

 that the mass of the negative carrier is always initially very small, 

 and its velocity consequently very great, and to account for the 

 disappearance of the negative in the C0 2 from the arc we would 

 require to assume that in C0 2 in the arc itself the mass travelling 

 with the carrier does not increase so rapidly as in air. 



(14) The experiment was tried of directing on the arc a blast 

 of gas so as to remove the carriers more rapidly from the neigh- 

 bourhood of the arc. In place of the wide tube D (Fig. 1) by 

 which the gas enters the funnel F, we substitute a tube of smaller 

 bore which projects into the funnel up to near the arc so that 

 a blast of considerable velocity impinges on the arc. With this 

 arrangement the negative carriers came off from the arc in much 



