﻿Dr. T. J. Baker on Breath Figures. 753 



The late Lord Rayleigh held the view that the part of the 

 glass swept by the flame hail been rendered cleaner than the 

 neighbouring portion, whilst Aitken urged that the track of 

 the flame had been rendered dusty by solid particles deposited 

 f i oni the flame, and that these particles aided condensation of 

 moisture. He pointed out that by scraping with a match- 

 stalk across the flume track a dusty deposit could be rubbed up, 

 and he considered that this contamination of the surface is 

 responsible for the breath figure. It is true that the track 

 which an ordinary blowpipe-flame has followed can be 

 detected by the eye before any moisture has been deposited 

 on the plate, but a flame of carbon monoxide leaves no such 

 deposit, and Aitken's explanation seems inadequate because 

 this flame yields an excellent breath figure. Lord Rayleigh 

 showed that it the outside of a test-tube were heated to 

 redness the "black" or transparent condensation could be 

 obtained on the correspondino- part of the interior of the 

 tube. This was at first contested by Aitken, who maintained 

 that the flame, or the hot gases from it, must strike the glass 

 directly to produce the result ; but further experiments led 

 him to accept Lord Rayleigh's statement, and he then sug- 

 gested that a chemical change in the glass itself might account 

 for the effect. 



Quincke found that when a drop of strong sulphuric acid 

 is warmed on a glass plate, which is afterwards washed and 

 dried, the " black " condensation may be obtained on the 

 part which has been exposed to the acid. Craig suggested 

 that this might be due to the soaking in of the acid, thus 

 forming a hygroscopic film; and as coal-gas always contains 

 sulphur compounds, he contended that a coal-gas flame 

 playing on glass might deposit enough sulphuric acid to act 

 in this way. But it was known that a flame of pure hydrogen 

 burning in air also gives breath figures, and Craig therefore 

 suggested the possibility that some nitric acid might be formed 

 by the flame, and that this acid might determine the pro- 

 duction of a breath figure. If this is true, it follows that 

 hydrogen burning in pure oxygen should fail to be effective. 

 This summary fairly represents the main features of our 

 knowledge of the subject up to 1913. From that date 

 onwards the author has intermittently carried on the inquiry, 

 with the result that other relevant phenomena have been 

 discovered, and a partial explanation of the results can be 

 offered. 



Phil. Mag. S. 6. Vol. 44. No. 2G2. Oct. 1922. 3 C 



