﻿760 Dr. T. J. Baker on Breath Figures. 



;md the other half was breathed upon. As soon as the 

 deposited moisture had evaporated the protecting cover was 

 removed, and the usual procedure for obtaining a transfer 

 in vacuo was followed. Not the slightest difference in the 

 two halves of the transfer could be detected. It is therefore 

 permissible, and sometimes convenient, to test the flamed 

 plate by breathing upon it before using it to obtain a 

 transfer. 



Length of time during which a flamed plate retains its 

 power of giving a transfer. 



A flamed plate was kept in a warm room for 60 hours, 

 and at the end of this time it was left in vacuo for 24 hours 

 in contact with a "cleaned" plate, and on this a good 

 transfer was obtained. Another mimed plate after 9 days' 

 exposure to the air behaved similarly, but the transfer was 

 fainter ; and in a third instance a plate produced a transfer 

 18 days after it had been flamed. The loss of the volatile 

 material is plainly very slow under ordinary conditions of 

 temperature and pressure. 



Condition of the flamed plate after it has been exposed 

 to reduced pressure. 



A flamed plate was left in vacuo for 24 hours. It was 

 then removed and clipped face to face with a " cleaned " 

 plate, and the two were kept in vacuo for 20 hours. No 

 transfer occurred, but the original flamed plate gave a 

 breath figure as good as though it had not been exposed to 

 low pressure. In a second trial the time allowed for transfer 

 in vacuo was extended to 48 hours, but no trace of transference 

 could be detected. 



These facts seem to confirm the hypothesis that transference 

 is due to the escape ot: material from the flamed track on the 

 plate, and that the whole of this escapes under reduced 

 pressure in the course of a day. At the same time it is 

 clear that the surface of the glass which has lost this matter 

 is still in an abnormal condition, and whatever this condition 

 may be it is one which persists for many weeks. 



Secondary transfer. 



A transfer was obtained in the usual manner. The plate A 

 on which this transfer had been effected was then clipped in 

 contact with a " cleaned " plate B, and both were placed 

 in vacuo for 10 minutes. At the end of this period they 

 were separated, and plate B was examined c No transfer 



