EGGS IN COLD STORAGE. 21 



The air is never perfectly saturated, not even when rain 

 is falling-; neither is it ever perfectly dry at any place. Rela- 

 tive humidity expresses relative amount of moisture in the air 

 only as long as the temperature of the air remains constant. 

 For this reason relative humidity is an imperfect datum. At a 

 low temperature, even a high relative humidity represents a 

 very small amount of vapor actually in the air, while a low 

 relative humidity at a high temperature represents a great 

 deal. 



The most important law relating- to above concise 

 statements, and one which, if carefully noted and 

 applied, will make, all work in humidity easily under- 

 stood, is best expressed thus: The capacity of air for 

 moisture is increased with its temperature.* 



At a temperature of 40 F., air will hold in sus- 

 pension more water vapor than at any lower tempera- 

 ture (see table); and when the difference is as much 

 as 10 F., the difference in the amount of moisture 

 the air will hold is very considerable. To illustrate: 

 Air which is saturated with moisture at 30 F., when 

 raised in temperature to 40 F., then holds but 68 per 

 cent of its total capacity. 



Under the head of "Temperature," it is stated . th 



that: "If eggs are held at a temperature of 30 F. in 

 an atmosphere of a given humidity, the growth of 

 fungus is less rapid than if held at any temperature 

 higher, with the same per cent of humidity. Refer- 

 ring again to the table, we see that a cubic foot of air, 

 when saturated at a temperatureof 40 F.,contains2. 85 

 grainsof water vapor, while at 30F. it contains but 1.96 

 grains, or only about two-thirds as much as at 40 F. 

 The same holds true with any relative humidity, the 

 same as when the air is saturated. Take, for instance, 

 air at a temperature of 40 F., with a humidity of 75 

 per cent, then a cubic foot of air holds 2.14 grains of 

 water vapor per cubic foot; and at a temperature of 



* Strictly speaking, air has no capacity for moisture, the water vapor being 

 simply diffused through the air, after the nature of a mechanical mixture. For 

 all practical purpases, we may regard it as being absorbed by the air, and it is 

 usually so treated. 



