SULPHURIC ACID FOR WATER. 369 
the maximum and minimum temperatures indicate, 
the evaporating force ranged from 1.03 to nearly 
1.9 inch of mercury, the acid allowed to evapo- 
rate none of the 14 grains of water with which I 
had diluted it. 
The experiments I have now related, offer con- 
clusive evidence, to those to whom such has 
hitherto appeared to be wanting, that vapour 
exists in air as a fluid swi generis ; or, that the 
evaporation of water is not owing to the exist- 
ence of a chemical affinity between the vapour of 
that liquid and atmospheric air. 
By those convinced that evaporation is not the 
consequence of a chemical affinity being exerted 
between vapour and air, two distinct notions have, 
in the case of evaporation from pure water, been 
entertained on the reason why evaporation does 
not goon so rapidly in air as in vacuo: one, 
that the retardation is owing to the weight of the 
atmosphere ; and the other, that it is owing to the 
vis inerti@ of the particles ef air; that vapour in 
ascending from the surface of water into the 
atmosphere, has to perform a circuitous route, 
similar to that which water has to take in descend- 
ing through pebbles; this reason being consi- 
3A 
