Hygroscopic mositure of flax seed and wheat and its relation to combine harvesting

This paper reports the results of experiments on the rate of absorption of hygroscopic moisture by seeds of flax and wheat exposed to atmospheres of different relative humidities, the rate of drying of wet seeds, the effect of an air current on the rate of drying, and the rate of absorption of free water by wheat. The absorption and loss of moisture by standing grain is of particular significance in relation to combine harvesting. Coleman and Fellows have shown that the final moisture content of the seeds of cereals and flax varies greatly when exposed for a long period (30 days or more) to atmospheres of different relative humidities (Fig. 1). Dry flax seeds absorb hygroscopic moisture somewhat more rapidly at first than wheat seeds (Fig. 2), and both flax and wheat seeds absorb moisture much more rapidly than do alfalfa seeds. Whole flax bolls absorb moisture approximately twice as rapidly as do the seeds (Fig. 3). The rapid absorption of hygroscopic moisture by the bolls probably explains why dry flax becomes difficult to thresh after a short period of high humidity. The rate of absorption of hygroscopic moisture by dry seeds (flax, wheat, and corn) varies with the temperature, at least within a certain range of temperature (Fig. 4). The rate of absorption is approximately twice as rapid at 30 degrees C as it is at 10 degrees C (Fig. 5). At 40 degrees C the rate of absorption is about the same as at 30 degrees C for a time, but later becomes slower, probably because the high temperature affects adversely the enzyme activity of the seeds. Wheat seeds containing 21% of moisture, based on dry weight, and flax seeds containing 14% will either absorb more moisture or lose moisture, depending upon the humidity of the air to which they are exposed (Fig. 7). In an atmosphere of 90% relative humidity such seeds absorbed moisture slowly, whereas at 75% relative humidity they lost moisture slowly. According to Coleman and Fellows, wheat will come to equilibrium at 17 to 18% of moisture and flax seeds at about 11.5% in an atmosphere of 75% relative humidity. The same results were obtained by the writer. Seeds of wheat of 38% and flax of 25% moisture content still absorbed moisture in a saturated atmosphere, but lost moisture in an atmosphere of lower relative humidity (Fig. 8). The seeds lost moisture rapidly in an atmosphere of 45% relative humidity. The curves are hyperbolic in form, flattening out as the moisture content approaches equilibrium. At 75% relative humidity the rate of drying of wheat was comparatively slow below 18% of moisture. The moisture content was reduced only 1%, that is, from 18.2 to 17.2%, from the 5th to the 7th days. This moisture content of 17.2%, based on dry weight, is equivalent to 14.7% based on wet weight, and the sample, therefore, was still too wet for safe storage. It is evident, therefore, that a relative humidity lower than 75% is necessary to insure the rapid drying of wet grain. An air current of about 500 cc per minute drawn through a U-tube containing wet wheat and flax seeds approximately doubled the rate of drying during a period of 8 hours, as compared with still air in a desiccator, both of 45% relative humidity. The absorption of free water by wheat is extremely rapid as compared with the absorption of hygroscopic moisture. The absorption of water at 25 degrees C is about 20 to 45% more rapid than at 10 degrees C (Table 4). The experiments reported indicate the significance of humidity in relation to the moisture content of grain which is freely exposed to the air. The results suggest a few points of practical importance, as follows: 1. It is certain that wet grain will not dry in an atmosphere of high relative humidity. 2. A relative humidity well below 75% appears to be necessary for effective drying. 3. Movement of the air, as by a breeze or wind, increases the rate of drying, provided, however, that the relative humidity is low enough to permit drying. 4. In air of high relative hu