148 



Miss E. W. Hobbs on the Change in the 



is shown in every case on the admission of air*. Except in the 

 curve F, which is separately discussed below, the rise continued 

 for not less than 25 minutes, and for most films still longer at 

 a slow rate. There is no fall in resistance in any of the cases 

 given to indicate that the process of ageing, which is shown 

 to a marked extent in curves A, B, and C, continues after the 

 admission of gas; but in some of the films investigated the 

 initial rise was followed by a very gradual decrease in 

 resistance. In such cases, the ageing was evidently still 

 continuing though at a decreased rate. It may therefore 

 be present in curves A, B^ and C though swamped by the 

 gas effect, and consequently the effect of the admission of gas 

 on these films cannot be examined with any certainty, since 

 the effect of ageing is quantitatively unknown. Fortunately 

 investigations have been carried out on films in which the 

 ageing was negligibly small. Curves D and E are examples 

 of these. Since they no doubt represent the true effect of 

 the air and, moreover, show extremes of magnitude, the 

 experimental numbers are given in Table II. 



Table II. 



Film D. 



Film E. 



Time in mins. 



Eesist. in ohms. 



Time in mins. 



Eesist. in ohms. 



00 



3100 



o-o 



1545 



150 



3090 



5-5 



1537 



300 



3090 



7-75 



1534 



40-0 



3090 



13-5 



1526 



410 



Air admitted. 



23-2 



1520 



41-75 



3187 



44-7 



1516 



423 



3200 



60-2 



1514 



44-4 



3218 



82-5 



1512 



453 



3223 



105-5 



1511 



475 



3229 



106-5 



Air admitted. 



49-4 



3234 



107-0 



1514 



52-75 



3229 



108-5 



1516 



5825 



3245 



110-0 



1517 



620 



3248 



1160 



1519 



730 



3254 



123-8 



1520 



84-7 



3258 



1360 



1521 



102-5 



3262 



154-3 



1522 



138-0 



3267 



4 hours later. 



1524 



16 hours later. 



3296 



Next morning. 



1526 



21 „ „ 



3297 







* It is possible that this might be missed if the experimental method 

 were such that the ageing was proceeding at a rapid rate at the moment 

 when the gas was admitted. 





