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



uncontaminated surface on which moisture condenses in the 

 form of a continuous transparent film. 



It would be expected that the flame-cleaned track would 

 speedily become contaminated again and cease to function, 

 but the extraordinary persistence of the property associated 

 with the production of a breath figure (p. 756) indicates that 

 other factors have to be considered. What these factors are 

 cannot be asserted with confidence, but it is not improbable 

 that the structure of the surface layer of the glass itself 

 suffers a change during its momentary exposure to a high 

 temperature, and it is also possible that some of the decom- 

 position products of the contaminating film are occluded by 

 the glass along the flame track. 



If a chemically cleaned sheet of glass is traversed by a flame 

 of carbon monoxide, and, when quite cold, is immersed in a 

 silvering solution, it is found that the silver begins to deposit 

 first along the flame track. Since no film of contamination 

 previously existed on the glass, it would appear that the 

 difference in the rate of deposition of silver is due to a 

 physical change in the surface of the glass. 



It is more difficult to offer an explanation of the trans- 

 ference of a breath figure from a flamed plate to a "cleaned" 

 plate, but since the process is hastened by reduction of pres- 

 sure and by rise in temperature, and occurs even when the 

 plates are not in contact, it is clear that some gaseous material 

 passes from one to the other. Also, it has to be borne in 

 mind that the transferred figure is an area from which 

 the contaminating film has been more or less removed 

 (p. 759). _ 



TV e may imagine that the contaminating film on a " cleaned " 

 plate tends to prevent the ready escape of gas-molecules 

 which have been occluded by the glass surface, but that 

 where this impediment has been removed by the passage of 

 a flame, or by sparks, a violent outrush occurs when the 

 temperature is raised or the pressure is reduced, and these 

 molecules on striking the opposed surface of the "cleaned " 

 plate break up and scatter that portion of the contaminating 

 film on which they impinge and thus expose a relatively 

 clean surface on which moisture will condense in the 

 "black" form. This suggestion may be extended to explain 

 a second transfer from the first. 



The molecules which are active in producing this result 

 probably arise from the occluded products of decomposition 

 of the contaminating film, for it has been found that no 

 transfer, or at most a very faint one, can be obtained from a 

 chemically clean plate which has been flamed. 



