TENSION OF AQUEOUS VAPOR 



335 



If the sample taken for analysis weighed half a gram, the per- 

 centage of nitrogen found would be 7.85. 



294. Tension of the Aqueous Vapor. It has been shown by 

 experience that when a gas is collected over a potash solution 

 containing 50 per cent, of potassium hydroxid, the tension of 

 the aqueous vapor is so far diminished as to be of no perceptible 

 influence on the final result. To correct the volume of a gas 

 for this slight tension would involve an unnecessary calculation 

 for practical purposes. If a gas thus collected should be trans- 

 ferred to a burette over mercury, on which some water floats, 

 then the correction should be made. 



At o the tension of aqueous vapor will support a column of 

 mercury 4.525 millimeters, and at 40 one 54.969 millimeters 

 high. 



The following table gives the tension of aqueous vapors in mil- 

 limeters of a mercurial column for each degree of temperature 

 from zero to 40. 



When a gas is in contact with water the aqueous vapor is dif- 

 fused throughout the mass, and the pressure to which the mix- 



