PROFESSOR TYNDALL’S CONTRIBUTIONS TO MOLECULAR PHYSICS. 355 
of caustic potash, in which the carbonic acid was intercepted, while the air charged 
itself with a little additional moisture. The absorption then observed amounted to 
203 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happened to compensate for the action of the carbonic acid withdrawn. 
The other component of the flame of Bunsen’s burner is carbonic acid ; and the radia- 
tion 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 0 0 
Undried air .... 10-0 16 T 
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 expe- 
rimental tube. The following results were obtained : — 
Table XXIX. — Air from the lungs containing C 0 2 . Source, carbonic-oxide flame. 
Tension in inches. 
Deflection. 
Absorption. 
1 
7-2 
12-0 
O 
O 
15-0 
25-0 
5 
20-0 
33-3 
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 surpassing delicacy the amount of carbonic acid emitted under various 
circumstances by the act of expiration. 
That pure carbonic acid is highly opaque to the radiation from the carbonic-oxide 
flame, is forcibly evidenced by the results recorded in the following Table. 
