58 



breathing fresh air even at low temperatures; also there may be injury 

 to furniture anil wood-work, but from our present standpoint the drier 

 the room air the better. In liaiiimiiy with this is the very noticeably de- 

 pressing effect of a very moist atmosphere. 



Let us now consider the numerical values concerned in these densitie;} 

 under ordinary cdnditions. 



Accepting Ilallibuiton's values for the composition of fresh air and 

 expired air both in the dry condition, 



Fresh air — 



Oygen 20.0ii per cent, by volume 



Nitrogen 79.00 per cent, by volume 



Carbon dioxide 0.04 per cent, by volume 



Expired air — 



Oxygen 16. 12 per cent, by volume 



Nitrogen 79.45 per cent, by volume 



Carbon dioxide 4 .43 per cent, by volume 



the densities, compared with hydrogen at the same temperature and pres- 

 sure, are 



rr u ■ . /20.96 16\ /7i).0() 14\ /0.04 22\ ,, ,r, 



Prcsh air: | x — | + l X — | + | X — 1=14.42 



V 100 1 / V 100 1 /\ 100 1 / 



r. ■ , ■ /16.12 16\ /79.45 14\ /4.43 22\ ,, ^^ 



Expired an-: ( Hr^T) + (^(r^T) + (wXY)"''-^' 



Considering now the effect of moist urt> on the density of expired air. 

 the tension of aipieous vapor, or vapor iiressure of water, is 47 nnlli- 

 meters of mercury at 37° C. (9S.(>° F. ), therefore any gas saturated with 



water vapor at this temperature consists of x or 0.2 T>er cent. 



TOO 1 



water v.-iiioi- and l(M)-().2 (U- 93.S per cent, by volume of all other constitu- 

 ents together. The composition of ('.xjiired air saturated with moisture 

 at body temperature is therefor(> 



Oxygen 10.12%. 93s. or l."..li: ]ier cent, by volume 



Nitrogen 79.45x.93S. or 74.52 per cent, by volume 



('ail)on dioxide 4.43x.93S, or 4. Hi per cent, by volume 



Water v.ipor 0.20 \>oi- cent, by volume 



'i'he density of this mixtni-e compjired with hydrogen at the same ivm- 

 peniture and pressure, calculated as before, the density of water vapor 

 being 9, i.s 14.33. 



