GRADE DETERMINATION. 17 



The mill for grinding (PL II, fig. 1) should be simple and strong 

 and easily taken apart for cleaning. An extra set of burrs is also 

 desirable, so that in case several samples need to be ground in close 

 succession the burrs may be changed before they have warmed enough 

 to heat the corn passing through. 



The aluminum pans are 4 inches in diameter and about 1 inch deep 

 and are used for holding the samples during the drying and weighing 

 process. 



In addition to the apparatus mentioned, there are also required some 

 few additional articles, such as a brush, forceps, and a smooth spoon 

 or spatula. 



METHODS OF DETERMINATION. 



The methods of determining the four elements mentioned may be 

 briefly described. 



MOISTURE. 



For determining the moisture a small sample of corn should be 

 ground into a coarse meal. If the corn is ground too line it becomes 

 heated during the operation and there is a consequent and irregular 

 loss of moisture. After grinding a definite quantity of the sample, it 

 should be weighed out in one of the aluminum pans. The larger this 

 quantity the less the percentage of error in weighing is likely to be. 

 However, for quick work the sample must not be too large. Twenty 

 or thirty grams has been found a convenient amount to use. This 

 weighed quantit} r , which for convenience in reckoning- should be an 

 even weight, either 20 or 30 grams, is then placed in the air-bath, 

 which has been previously heated to about 102° C. (215° F.). This 

 temperature is slightly above the boiling point of water and will 

 quickly evaporate the moisture, and after subsequent weighing the 

 percentage of loss ma}^ be determined. Theoreticall}' the sample 

 should be dried until repeated weighings would show no further 

 decrease in weight, but for practical purposes, where the element of 

 time required for making these determinations is important, a shorter 

 time will suffice. It has been found by numerous experiments that 

 the amount of moisture which a sample of coarsely ground meal will 

 give up during two hours' drying at 102° to 105° C. (215° to 221° F.) 

 is about 1£ per cent less than the total amount of moisture contained, 

 so that for commercial purposes two hours 1 drying at the above tem- 

 perature will yield results from which the total moisture can be esti- 

 mated with sufficient accuracy for general work. It is necessary, 

 however, to extend this time to three hours on days when the atmos- 

 phere is especially damp. Whenever immediate results are not abso- 

 lute^ necessary, it is much safer and more satisfactory to dry the 

 sample completely; that is, to dry it until repeated weighings show no 

 further loss. This commonly requires twelve to sixteen hours. After 



26159— No. 41—03 2 



