Analysis of the Human Breath. 115 



breath. As the absorptions in the two cases were equal, the 

 percentage of carbonic acid in the breath could be readily found. 

 The following Table shows how far experiment corroborated 



theory : — 



Table VII. — Source : Carbonic oxide flame. 



Pure carbonic acid gas. Absorption per 100. 



2*5 inches 54*5 



40 inches 57*7 



30-0 inches 70-0 



Referring to Table V., we see that 30 inches of breath from 

 bag No. IV. absorbed 54 per cent, of the whole radiation. The 

 nearest approach to this absorption is the first in the above 

 Table, and from this we may roughly assume that about 2'4 

 inches of pure carbonic acid gives about the same absorption as 

 30 inches of dried breath. The following proportion should then 

 give the amount of carbonic acid in the breath from bag No. IV., 



30 : 100 : : 2*4 : 8, 



from which it appears that tjie breath in bag No. IV. contained 

 8 per cent, of carbonic acid. Chemical analysis shows us that 

 there is but 5*2 per cent, of carbonic acid in this specimen of 

 breath. Here is at once a formidable difficulty, It would be 

 impossible to doubt the correctness of Dr. Frankland's analysis, 

 for 8 per cent, is far beyond the average amount of carbonic acid 

 found in expired air, yet at the same time the absorption was 

 most accurately determined and confirmed by repeated experi- 

 ments. Could any of the conditions of experiment in the two cases 

 have been different ? It was just possible that the burner in the 

 lamp might have been moved ; and if raised, the radiation from 

 the heated jet would probably come into play and thus slightly 

 alter the character of the source. The burner was therefore 

 lowered a quarter of an inch, and in this position the following 

 observations were made : — 



Table VIII.— 



Pure carbonic acid gas. 



Tension, in 





Absorption 



inches. 



Deflection. 



per 100. 



10... 



. 28-2 



45-5 



1-5 .. . 



. 31-5 



50-8 



20... 



. 330 



53-1 



25 .. . 



. 34-5 



55-6 



30... 



. 35-5 



57-2 



Total heat . 



. 450 



1000 



12 



