26 CONSTRUCTIVE BEEKEEPING 



can be obtained in a way that conserves the heat of a hive, a step 

 forward has been taken. This will result if we let the bees, as 

 they are striving to do, use their hive as a condenser. 



To understand how water vapor is condensed in a hive, the 

 dewpoint should be understood. Saturated air is at the dewpoint. 

 The amount of moisture that the air will hold varies as the tem- 

 perature changes. The amount of moisture in the air is spoken 

 of as absolute humidity. Air at degrees F. is saturated with 

 1-2 grain, at 60 degrees F. 5 grains, and at 80 degrees F. with 11 

 grains of water vapor. Air at 60 degrees which contains but 

 2 1-2 grains of gater vapor would be at 1-2 or 50 per cent of sat- 

 uration. Air at 78 degrees which contains the same amount of 

 water vapor (2 1-2 grains) would be but 1-4 or 25 per cent satur- 

 ated. This per cent of saturation is called relative humidity. If 

 the amount of water vapor in the air remains constant as the 

 temperature changes, the relative humidtiy changes with the 

 temperature. Air that is saturated at 78 degrees would have to 

 give up 50 per cent of its water vapor when its temperature is 

 reduced to 60 degrees, leaving this 60 degree air also saturated. 



The dewpoint is the temperature of the air, at which it would 

 be at saturation, if the amount of moisture is neither increased 

 nor deminished. 



To illustrathe the principle of the air giving up part of its 

 water vapor when its temperature is reduced to the dewpoint, 

 saturate a sponge with water, then press slightly on it and it 

 looses part of its water. The pressure of the hands acts on the 

 sponge the same as reduced temperature on saturated air. 



The most obvious illustration of this formation of dew, or 

 condensation of moisture on a cool surface, is when a pitcher of 

 ice water is placed in a warm room. This everybody is familiar 

 with. Condensed vapor on the windows, when the outside tem- 

 perature is cool, is another. Place a pan, bottom up on the ground 

 and dew will be found on the inside surface of the pan in the 

 morning. 



The beehive, when we allow the bees to arrange their own 

 ventilation, condenses vapor this way, when there is enough dif- 



