520 Prof. Tyndall's Contributions to Molecular Physics. 



then observed amounted to 



20-3 per cent, 

 of the entire radiation. The exact agreement of this with the 

 last result is, of course, an accident ; the additional humidity of 

 the air derived from the solution of potash happened to compen- 

 sate for the action of the carbonic acid withdrawn. 



The other component of the flame of Bunsen's burner is car- 

 bonic acid ; and the radiation of this substance is immediately 

 obtained from a flame of carbonic oxide. With the air of the 

 laboratory the following results were obtained : — 



Table XXVIII. — Radiation through Atmospheric Air. Source, 

 carbonic-oxide flame (very small). 



Deflection. Absorption. 



Dry air 



Undriedair. . . . 1(H) 16«1 



Of the heat emitted by carbonic acid, 16 per cent, was absorbed 

 by the common air of the laboratory. After the air had been 

 passed through sulphuric acid, the aqueous vapour being thus 

 removed while the carbonic acid remained, the absorption was 

 13"8 per cent. 



An india-rubber bag was filled from the lungs ; it contained 

 therefore both the aqueous vapour and the carbonic acid of the 

 breath. The air from the bag was conducted through a drying 

 apparatus, the mixed air and carbonic acid being permitted to enter 

 the experimental tube. The following results were obtained : — 



Table XXIX. — Air from the lungs containing CO 2 . Source, 

 carbonic-oxide flame. 



Tension in inches. 



Deflection. 



Absorption, 



1 



o 



7-2 



120 



3 



15-0 



25-0 



5 



20-0 



333 



30 



30-8 



50-0 



Thus the tube filled with dry air from the lungs intercepted 

 50 per cent, of the entire radiation from a carbonic-oxide flame. 

 It is quite manifest that we have here a means of testing with sur- 

 passing delicacy the amount of carbonic acid emitted under 

 various circumstances by the act of expiration *. 



That pure carbonic acid is highly opake to the radiation from 

 the carbonic-oxide flame, is forcibly evidenced by the results 

 recorded in the following Table. 



* [See article by W. F. Barrett " On a Physical Analysis of the Human 

 Breath," at p. 108 of the present volume, — Ed, J 



