Analyfts oj the Air. 249 
time fubfide and fall flat, if they were not 
frequently replenifhed with frefh elaftick 
air at every infpiration, thro’ which the in- 
ferior heated vapour and air afeends, and 
leaves room for the frefli air to defeend in- 
to the veficles, where the heat of the lungs 
make it expand about 4 part $ which degree 
of expanlion of a temperate air, I found by 
inverting a fmall glafs bubble in water, a 
little warmer than a Thermometer is, by hav- 
ing its ball held fome time in the mouth, 
which may reafonably be taken for the de- 
gree of warmth in the cavity of the lungs. 
When the bubble was cool, the quantity of 
water imbibed by it was equal to 4 of the 
cavity of the whole bubble. 
But when inftead of thefe frequent re- 
cruits of frefh air, there is infpired an air, 
furcharged with acid fumes and vapours, 
which not only by their acidity contrad the 
exquifirely fenfible veficles, but alfo by their 
groffnefs much retard the free ingrefs of the 
air into the veficles, many of which are ex- 
ceeding fmall, fo as not to be vifibie with- 
out a microfeope 5 which fumes are alfo 
continually rebating the elafticity of that 
air ; then the air in the veficles will, by Ex* 
per. 107, and 108, lofe its elafticity very 
faff, 
