Decemjjee 4, 1908] 



SCIENCE 



813 



crosses the 75° line at a point corresponding 

 to 13.95 per cent, of moisture. This state- 

 ment assumes, of course, that the measure- 

 ments were made with electrodes of standard 

 size, to which this chart is only applicable. 



Apparatus for Measuring Electrical Be- 

 sistance of Grain. — Unless the grain is very 

 wet, its specific electrical resistance is very 

 high. The resistance, while electrolytic in 

 character, is so great that polarization is not 

 troublesome, and measurements can be made 

 with direct currents. The electrical apparatus 

 required for such measurements is therefore 

 similar to that used for testing the insulation 

 of cables. The measurements described were 

 made principally with a Wheatstone bridge, 

 using a fairly sensitive galvanometer, and an 

 electromotive force of seventeen volts. In the 

 driest samples (below 12 per cent.) the resist- 

 ance was so high, that it could not be 

 measured by this method. For these samples, 

 the direct deflection method was used, the 

 galvanometer and grain resistance being con- 

 nected in series with a battery having an elec- 

 tromotive force of ten volts. 



In all the measurements described, the elec- 

 trodes used consisted of two parallel one 

 half inch round brass rods, one and one 

 half inches between centers, and twelve inches 

 long. These rods were kept parallel and in- 

 sulated from each other by being supported in 

 a hard-rubber block at their upper ends. Con- 

 necting wires with extra heavy rubber insula- 

 tion were soldered to the two upper ends of 

 the electrodes. The grain during measure- 

 ments was held in glass battery jars five inches 

 in diameter and eleven inches high. The 

 height of the grain, inside measurement, was 

 ten inches. The lower ends of the electrodes 

 rested upon the bottom of the jar. The 

 temperature was measured with a mercurial 

 thermometer having a cylindrical bulb, which 

 could be readily forced into the grain. 



Before each measurement, the electrodes 

 were removed, and the grain was packed by 

 jarring the bottom of the container against 

 some solid object. It is important that this 

 precaution in packing be observed if satis- 

 factory results are to be obtained. This will 

 not be necessary in measurements made in 



cars, since the settling of the grain in transit 

 will have reduced it to a stable condition. 



Portable cable testing sets can be used for 

 the resistance measurements necessary for 

 moisture determinations, providing the grain 

 is not too dry. A special testing set is now 

 being constructed in which a resistance coil 

 for determining the temperature of the grain 

 is placed within one of the electrodes. A 

 shunt box for use in connection with the 

 direct deflection method is also being con- 

 structed. 



This method is similar in principle to that 

 developed some years ago in the Division of 

 Soils for the measurement of the moisture 

 content of soils.' The difficulties that de- 

 veloped in connection with that method, 

 namely, the translocation of salts and the 

 cracking away of the soil from the electrodes, 

 are not encountered in the measurement of 

 the moisture content of grain. There is a 

 possibility that wheat grown in different 

 localities will show a sufficient variation in 

 salt content to affect the moisture determina- 

 tions, but such variation has not been indi- 

 cated in the samples so far examined. 



Summary. — This paper deals with an elec- 

 trical resistance method for the rapid determi- 

 nation of the moisture content of grain. The 

 experiments have so far been confined to 

 wheat. The electrical resistance of wheat 

 containing 13 per cent, of moisture is fifty 

 times that of wheat containing 15 per cent. 

 The temperature of the grain must be de- 

 termined. The results of the experiments in- 

 dicate that the moisture content can be de- 

 termined by this method with a probable 

 error not exceeding 0.3 per cent. Measure- 

 ments can be made rapidly, requiring only 

 two or three minutes. The apparatus is port- 

 able in character so that measurements can be 

 carried on in cars or elevators as well as in 

 the laboratory. The use of this method in 

 connection with other grains and grain 

 products is now being investigated. 



Lyman J. Briggs 



Physical Labobatort, 



Btjeeau of Plant Industry, 

 October 17, 1908 



° Bulletin 6, Division of Soils. 



