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



red-hot spot was visible. When quite cold the face of the 

 plate remote from the flamed face was placed in contact with 

 a " cleaned'''' sheet of glass, and both were subjected to 

 reduced pressure. No transfer was visible even after the 

 lapse of 46 hours. A similar negative result is obtained if 

 the flamed face of the silica plate is used. 



Electric breath figures. 



The tracks of electric sparks which have traversed the 

 surface of a " cleaned "plate of glass are rendered visible by 

 " black " condensation when the plate is breathed upon. 

 Figures so obtained are transferable, and in all their pro- 

 perties resemble those produced by flames. 



Electric discharges in air produce ozone, but the present 

 Lord Rayleigh has shown that'this gas does not yield breath 

 figures on glass. 



Nitric acid is also formed, but the author has found that 

 good figures can be obtained on glass which has been tra- 

 versed by sparks in an atmosphere of hydrogen. It is 

 therefore unlikely that the figures are caused either by 

 ozone or nitric acid. By passing a large number of sparks 

 between two platinum sheets which rested upon a sheet of 

 " cleaned " glass a well-defined area was obtained, which 

 could be tested for friction by Hardy's method. To cause 

 steady motion on the unsparked portion of the glass a pull of 

 4|- grams on the watch-glass was sufficient, whilst on the 

 sparked area a force of 1\ to 8 grams weight was necessary 

 to start motion. These results are almost identical with 

 those obtained on the track left by the flame of carbon 

 monoxide (p. 757), and it is highly probable that sparks 

 remove the contaminating film from the glass surface either 

 by their heating or disruptive effects. 



It is well known that when a sheet of cleaned glass is 

 placed upon an insulated metal plate which is connected to 

 one pole of an induction-coil, and a coin, connected to the 

 other pole, is laid on the glass, the passage of a discharge for 

 a few seconds will produce the conditions for the development 

 of a breath figure on the glass. The " black "' condensation 

 corresponds to those parts of the coin which are in relief and, 

 in addition, the tracks of any sparks which may have traversed 

 the glass surface from the edge of the coin will also be 

 rendered evident as wavy lines of " black " condensation. 



It may be assumed that discharges from the under surface 

 of the coin to the glass beneath it occur most abundantly 

 from those parts which are in highest relief, so that the film 



