tempered to 15 per cent moisture on the invisible losses occurring 
during the milling process and on the total yield of mill products; 
also the influence of the temperature of the air within the mill upon 
the total yield of mill products. 
HUMIDITY. 
That the humidity of the atmosphere in the mill influences milling 
results is commonly known to millers. This influence, however, the 
miller is able to -control to a certain extent by varying the tempering 
or conditioning process applied to the wheat and the manner of 
grinding and bolting, provided he can anticipate any change that 
is likely to take place in the humidity of the atmosphere. Advance 
information of the weather, however, can not alwa} T s be depended 
upon ; consequently, the miller can not always have his wheat condi- 
tioned and his mill adjusted properly for obtaining the highest de- 
gree of efficiency possible. Certain atmospheric conditions are gen- 
erally recognized as being more conducive to good milling results 
than others; therefore, the installation of means for controlling the 
condition of the atmosphere within the mill would give to the miller 
a greater degree of control over the operation of his plant and there- 
by improve his results. 
NORMAL MOISTURE CONTENT. 
Evidence that an approximate parallelism exists between the mois- 
ture content of wheat and the relative humidity 1 of the atmosphere 
lies in the well-known fact that the normal moisture content of air- 
dry wheat is higher when stored in moist climates than when stored 
in dry climates. The term " normal " as used in this bulletin means 
that moisture content which is unaffected by continued exposure to 
the prevailing atmospheric conditions. In other words, it is that 
point at which equilibrium is established between the moisture con- 
tent of the wheat and the humidity of the air. According to experi- 
ments by Stockham, 2 the moisture content normal for different wheats 
1 The amount of water vapor which can be mixed with a given quantity of air varies 
with its temperature ; the higher the temperature, the greater the amount of water vapor 
it can hold. When air at a given temperature contains all the moisture possible for it 
to hold, it is said to be saturated. The percentage or ratio of the actual amount of 
moisture contained by a cubic unit of air to the amount which the same air would hold 
at the same temeprature if sa-turated is called the relative humidity. Relative humidity 
is usually stated in terms of percentage. 
Since the capacity of the air for water vapor increases proportionately with tem- 
perature, every increase in temperature, assuming that the quantity of water vapor in 
the air remains the same, results in a lowering of the relative humidity, and every 
decrease in temperature results in a proportionate increase of relative humidity until 
the saturation point is reached, beyond which condensation occurs. 
2 Stockham, W. L., The Capacity of Wheat and Mill Products for Moisture. North 
Dakota Agr. Exp. Sta. Bui. No. 120, 1917. 
