20 



EGGS IN COLD STORAGE. 



what relative To enable us to thoroughly understand the mean- 

 humidity . J 

 signifies. mg- of relative humidity, as it is called, we will study 



a few extracts from " Instructions to Voluntary Ob- 

 servers," issued by the Weather Bureau at Washing-- 

 ton, D. C. Humidity is considered on a decimal scale, 

 with 100 the saturation point of the air, at which it 

 will hold no more water vapor, and the point at 

 which air contains no moisture whatever. The vari- 

 ous percentag-es between these points is a degree of 

 humidity relative to these two extremes, or relative 

 humidity. The quotations below are not contained 

 in the recent issue of instructions, but are from the 

 issue of 1892, which is now superseded by that of 1897. 



Quoted from 

 "Instructions 

 to Weather 

 Observers." 



WATER VAPOR IN AIR. 



The air contains vapor of water, transparent and color- 

 less like its other g-aseous components. It only becomes visible 

 on condensing to fog" or cloud, which is only water in a fine 

 state of division. The amount is very variable at different 

 times, even in the vicinity of the ocean. The amount of moisture 

 that can exist as vapor in the air depends on the temperature. 

 There is a certain pressure of vapor, corresponding- to every 

 temperature, which cannot be exceeded ; beyond this there is 

 condensation. This temperature is called the temperature of 

 saturation for the pressure. When the temperature of the air 

 diminishes until the saturation temperature for the vapor con- 

 tained is reached, any further fall causes a condensation of 

 moisture. The temperature at which this occurs is called the 

 dew point temperature of the air at that time. The less the 

 quantity of moisture the air contains, the lower will be the 

 temperature of the dew point. For different saturation temper- 

 atures, the weight of vapor, in grains, contained in a cubic 

 foot of air is as follows: 



Temperature of 

 Saturation, Degrees F. 





 10 

 20 

 30 

 40 

 50 

 60 

 70 

 80 

 90 

 100 



Weig-ht in a 

 Cubic Foot, Grains. 



0.56 



0.87 



1.32 



1.96 



2.85 



4.08 



5.74 



7.98 

 10.93 

 14.79 

 19.77 



