ADIABATIC CHANGES OF MOIST AIR NEUHOFF 



475 



which equation leads us to the construction of the isothermal curves 

 of saturation shown in fig. 4. 



By using pressure and temperature as coordinates the adiabats 

 of the dry stage and of the condensation stage as well as the gram- 

 lines may all be combined in one diagram, by the use of which it 

 becomes possible to determine all the adiabatic changes of moist air 

 in successive series. Such a system of curves is shown in fig. 5. 



/O 15 



300 m / 



700 



760 



FIG. 4. ISOTHERMS OF 

 SATURATION 



-20° - /() (J° /O" 20° M° 



FIG. 5. DIAGRAM OF ADIABATS 



Every point of the saturation curve that corresponds to a definite 

 condition p, t shows how many grams of aqueous vapor are con- 

 tained in (1 + x) kilograms of saturated air. For instance, at 30 

 temperature and 76o mm pressure we have the gram line for 27 

 grams. If this air is still in the dry stage and if the mixing ratio 

 is 10 grams, then from the ratio 



10 x 100 



27 



we obtain the relative humidity, 37 per cent. 



Conversely if for 20 and 76o mm of pressure we have 20 per cent 

 as the relative humidity then, since the saturation curve at this 

 point is 15 grams, we find the mixing ratio to be 



15 X 20 

 100 



= 3 grams. 



The expansion continues along the adiabat of the dry stage until 

 the point of saturation is reached, that is to say, until the adiabat 

 of the dry stage intersects the gram line that corresponds to the 

 mixing ratio. 



