Deoembeb 4, 1908] 



SCIENCE 



811 



description of the method is given. Cor- 

 responding measurements will he made for 

 other grains as well as for flour and corn- 

 meal. A portable apparatus suitable for 

 measurements in cars and elevators is also be- 

 ing constructed. 



Description of the Electrical Resistance 

 Method for Measuring the Moisture Content 

 of Grain. — This method consists essentially in 

 the measurement of the resistance offered to 

 the passage of an electric current through the 

 grain from one metallic electrode to another. 

 The electrical resistance decreases rapidly as 

 the moisture content of the grain increases. 

 The electrical resistance of wheat containing 

 13 per cent, of moisture is seven times that 

 of wheat containing 14 per cent, and fifty 

 times that of wheat containing 15 per cent, of 

 moisture. This method, therefore, gives a 

 very open scale, and a considerable variation 

 in resistance can take place without seriously 

 affecting the accuracy of the moisture de- 

 terminations. 



The relation between the electrical resist- 

 ance and the moisture content of wheat is 

 shown graphically in Fig. 1. The moisture 

 percentages in this figure are plotted as ordi- 

 nates and the natural logarithms of the cor- 

 responding resistances are plotted as abscissas. 

 Five widely differing types of wheat, inclu- 



FlO. 1. Chart showing the Relation between 

 the Moisture Content and the Electrical Resist- 

 ance of Wheat. Measurements made at 75° F. 

 For description of electrodes see text. Resistances 

 expressed in megohms. Moisture percentages 

 based on weight of moist grain. 



ding soft red winter, hard red winter, No. 1 

 hard spring, durum, and a badly mixed wheat 

 containing many weed seeds, were used in 

 these determinations. The closeness with 

 which the different points on the diagram ap- 

 proach the straight line drawn through them 

 illustrates the accuracy with which moisture 

 determinations can be made by this method. 

 The logarithms of the resistances instead of 

 the resistances themselves are plotted in this 

 diagram in order to condense the diagram, 

 and to show the linear relation between the 

 two variables. 



Relation of Electrical Resistance to Tem- 

 perature. — The electrical resistance of wheat 

 is also dependent upon the temperature of 

 the grain. In fact, the rapidity with which 

 the resistance decreases as the temperature in- 

 creases is quite remarkable, and greatly ex- 

 ceeds that occurring in most substances. The 

 change in the electrical resistance of wheat 

 with the temperature is shown graphically in 

 Fig. 2, in which temperatures are plotted as 

 ordinates and electrical resistances as ab- 

 scissas. The resistance at 4° C. is seen to be 

 eighteen times the resistance at 24° 0. This 

 curve is based upon 34 groups of measure- 

 ments made upon hard red winter, soft red 

 winter, hard red spring, durum, and a mixed 

 wheat. Dots on the diagram refer to one 

 sample, crosses to another, and so on. In 

 order to construct a mean temperature resist- 

 ance curve, the resistances corresponding to 

 the different samples were all increased or de- 

 creased by an amount corresponding to the 

 mean of the ratios of the resistances to the 

 corresponding resistances of one curve taken 

 as a standard. In making these determina- 

 tions, the wheat, after being cooled in an ice 

 chest, was allowed to approach the tempera^ 

 ture of the room, and a series of resistance 

 measurements was made as the temperature 

 increased. The grain was in each case stirred 

 to obtain as uniform a temperature distribu- 

 tion as possible before each set of measure- 

 ments. Temperatures above that of the room 

 were obtained in a similar manner by heating 

 the grain and measuring the resistance as it 

 cooled. It is difficult to determine the true 



