Analysis of the Human Breath. Ill 



our atmosphere was easily measurable, and far exceeded the 

 absorption by the aqueous vapour. The quantity of this latter 

 gas is about 35 times the quantity of carbonic acid, and yet 

 the generally feeble carbonic acid intercepts nearly 8 per cent, 

 more of the radiation from a carbonic oxide flame. Taking 

 the average state of our atmosphere as containing by volume 

 4 parts of carbonic acid and 140 parts of aqueous vapour in 

 every 10,000 parts of air, and estimating the quantities of 

 these gases present in the laboratory at the time of experiment 

 at double this amount, the absolute quantities contained in the 

 experimental tube and producing the above absorptions are found 

 to be '18 cubic inch of carbonic acid and 6*3 cubic inches of 

 aqueous vapour, the capacity of the tube itself being 225 cubic 

 inches. 



In the memoir by Professor Tyndall referred to at the com- 

 mencement, it was stated that the degree of accord between the 

 oscillating periods of the molecules of a source of heat and those of 

 a body placed in the path of its rays, determines the amount of ab- 

 sorption which those rays will undergo in passing through the in- 

 terposed substance. This statement is illustrated in the foregoing 

 experiments, whilst it was confirmed by substituting for the flame 

 of carbonic oxide a small flame of hydrogen. Here, as before, air 

 passed over potash and sulphuric acid showed only slight dynamic 

 radiation ; common air sent direct from the laboratory into the 

 tube gave a deflection of 6°, or an absorption of 10 per cent. 

 In the next experiment the air was dried by passing over sul- 

 phuric acid ; the needle in this case showed no absorption what- 

 ever, the same amount of heat reaching the pile when the tube 

 was filled with dry air as when the tube was exhausted. To 

 complete the comparison, air was drawn into the tube after 

 being deprived of its carbonic acid ; here a deflection of 2 C, 5 was 

 found, or 4*4 per cent, absorption. 



The following Table shows these results placed side by side : — 



Table I. 



Source : 



Air passed over potash and"[ 



sulphuric acid . 

 Air direct into tube 

 Air minus aqueous vapour 

 Air minus carbonic acid . 



The day on which these measurements were made was remark- 



r~ 





— -\ 



Carbonic oxide flame. 



Hydrogen flame. 



Deflec- 



Absorp- 



Deflec- Absorp 



tion. 



tion. 



tion. tion. 



nd }d-o 



. 9-3 



o-o 



do o-o 



15-0 - 



60 100 



ir . 8-7 



13-8 



o-o o-o 



. 40 



6-4 



2-5 4-4 



