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, fro.m 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 



