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



When the tube was cold a silvering solution was introduced, 

 and the quality of the mirror obtained was better on the zone 

 which had been heated than elsewhere. The borders of this 

 belt were badly silvered, and it seems probable that the con- 

 taminating film which covered the interior of the tube had 

 been driven from the heated belt to the cooler parts on each 

 side of it, where the increased contamination would affect 

 the deposition of silver adversely. 



If the tube has been heated until softening is imminent, 

 the silver deposits on this part in a manner which suggests 

 that the original smoothness of the glass surface has been 

 partially destroyed. 



The point which was at issue between Lord Rayleigh and 

 Aitken appears therefore to be decided in favour of the 

 former, who believed that the passage of aflame across the 

 glass cleanses it, and thus favours the condensation of moisture 

 in the form of a continuous film instead of droplets. 



Nitric acid not a cause of breath figures. 



It remains to consider the suggestion of Craig, viz. that 

 some nitric acid might be formed in a flame and be deposited 

 on the glass, thus determining the formation of a breath 

 figure. If hydrogen were burnt in pure oxygen this possi- 

 bility would be excluded. A jet of hydrogen was ignited 

 electrically in a large tube through which a stream of oxygen 

 was passing, and by a simple device a small glass sheet was 

 passed through the flame. The glass showed an excellent 

 breath figure when breathed upon. The oxygen used was 

 prepared in one case from sodium peroxide and water, and 

 in another experiment from potassium permanganate, but 

 absorption with pyrogailol showed that it contained rather 

 more than 1 per cent, of (presumably) nitrogen. The result 

 is not conclusive, because a small amount of nitric acid might 

 have been formed ; but it seems unlikely that the reduction 

 of the nitrogen from 79 per cent, (in air) to about 1 per cent, 

 should have been without influence on the strength of : the 

 breath figure if nitric acid plays any part in the process ; 

 and it is difficult to see how the presence of a minute quantity 

 of acid could account for the great increase in friction 

 described in the preceding section. 



Transference of breath figures to a second plate. 



In that which follows it will be convenient to refer to 

 a plate which lias been traversed by a flame as a " flamed ,J 

 plate. 



