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



Experimental. 



With the exception of certain cases specifically mentioned, 

 the surfaces used were first washed with soap and water, 

 then rinsed with tap-water, dried with a clean cloth, and 

 finallyrubbed vigorously with a clean linen handkerchief until 

 the white condensation produced by breathing lightly upon 

 them showed uniformity. The surfaces so prepared will be 

 described for convenience as " cleaned " surfaces. It must 

 also be understood that the term " breath figure " connotes 

 that condition of a surface which reveals itself by the black 

 form of condensation. A breath figure is not visible until 

 moisture condenses on the surface. 



At the outset it seemed probable that a complex substance 

 like glass was not best suited for the purpose, and some pre- 

 liminary experiments were made with other materials. In 

 general, it was found that the chemical composition of the 

 substance is not important, because breath figures were easily 

 obtained on porcelain, rock-crystal, mica, Iceland spar, 

 platinum, nickel, silver, brass, and mercury. Aitken's sug- 

 gestion that chemical change might explain the effect cannot 

 be maintained in face of the fact that the figures can be 

 obtained on rock-crystal and platinum. Again, since the 

 burning of coal-gas in a blowpipe-flame might lead to the 

 deposition on a cold surface of such substances as carbon, 

 sulphur compounds, and tarry matter, it w r as decided to try 

 the flames of hydrogen and carbon monoxide. Hydrogen 

 prepared from hydrochloric acid and magnesium was passed 

 through soda-lime to arrest any acid spray, and was burnt at 

 a platinum jet. This flame produced excellent breath figures. 

 Burning carbon monoxide from sodium formate and sulphuric 

 acid gave equally good figures. From these experiments 

 we may conclude that breath figures do not require for 

 their production the deposition of any solid matter from 

 the flame. Further,, since no water is produced when carbon 

 monoxide is burnt, the effect cannot be attributed to depo- 

 sition of moisture. 



Lord Bayleigh has pointed out that the pattern of a breath 

 figure may be recorded permanently by the chemical depo- 

 sition of silver on the glass plate. The track of the flame is 

 distinctly marked by a difference in the appearance of the 

 deposit, and this difference is most marked near the margins 

 of the track, i. e. where the hottest part of the flame 

 impinges on the glass. This was confirmed both when the 

 flames of hydrogen and coal-gas were employed. 



