INFLUENCE OF RELATIVE HUMIDITY AND MOISTURE CONTENT. 3 
and for their various mill products varies somewhat, even under the 
same atmospheric condition. 
In milling, the practice of adding moisture to wheat in its prepara- 
tion for grinding, which is usually referred to as tempering, may 
give to the wheat a moisture content above normal for the prevailing 
atmospheric conditions. Whenever this occurs and the wheat is ex- 
posed to the air, evaporation of this excess moisture begins. The 
quantity of moisture, however, actually evaporated from the wheat 
during milling is dependent upon a number of variables, including 
the quantity of moisture in excess of that normal for the prevailing 
atmospheric conditions, the distribution of the moisture, the length of 
time the material is exposed, the manner of exposure, the circulation 
of air, and the character of the material. Furthermore, because of 
the heat generated by the action of the various machines used in mill- 
ing and other causes, the relative humidity of the air in different 
parts of the mill varies somewhat, affecting the rate and extent of 
the evaporation taking place at different steps in the milling process. 
MATERIAL AND METHOD OF EXPERIMENTS. 
The wheats used in the experiments conducted by the Bureau of 
Markets and Crop Estimates were milled on a special-type reduction 
machine, consisting of four pairs of 6-inch rolls, three corrugated and 
one smooth, together with a sifter and sieves appropriate for making 
the various separations of stock required. The quantity of wheat 
used in each test was 1,500 grams, or approximately 3 pounds. The 
wheats tested were hard wheats, representing various grades, quali- 
ties, and varieties, from various parts of the United States. 
The system of milling used, although not the continuous automatic 
system employed in commercial mills, included all the various steps 
deemed necessary in modern milling practice. Figure 1 represents 
the flow sheet of the system used. 
The time required to make each test averaged 1^ hours, which 
incidentally represents the period of time that each sample was 
exposed to the atmospheric conditions prevailing in the room in 
which the milling was performed. Before milling, each sample was 
cleaned, scoured, and tempered. No cleaning or scouring was per- 
formed after tempering. A determination of the moisture content 
of each cleaned and scoured sample was made previous to tempering. 
The tempering period ranged from 18 to 22 hours. The amount of 
temper water added depended upon the moisture content of the 
individual samples, enough being added to raise the moisture content 
to 15 per cent. During tempering, the samples were kept in air-tight 
cans which prevented any loss of moisture from the wheat from the 
beginning of the tempering period until the wheat started through 
