16 THE COMMEECIAL GRADING OF CORN. 



and having the.se four generally understood there is available a basis 

 for uniformity which has not up to this time been offered to the trade. 



APPARATUS REQUIRED. 



The apparatus required for measuring the elements mentioned 



above is as follows, the prices given being approximate: 



One balance, with weights $33. 00 



One copper oven, or air-bath 12. 00 



One centigrade thermometer 1. 25 



One gas heater " 1-00 



One metal sieve, with top and bottom 2. 35 



One coffee or spice mill 1. 75 



One set of aluminum pans, at 40 cents each, about 4. 80 



Miscellaneous apparatus 1-00 



Total estimated cost 57.15 



The balance should be as accurate as possible, since the most impor- 

 tant part of the work depends upon results obtained by its use. It 

 should be sensitive to 10 milligrams or less. A very compact and 

 satisfactory balance is shown in PI. II, fig. 2. 



The oven or air-bath (PI. I) is simply a copper box covered with 

 asbestos, having a large door and with two holes in the top, through 

 one of which the thermometer is suspended. The bath contains a shelf 

 upon which the pans of material may be placed during the drying 

 operation. When an electric heater is used it may be placed inside, 

 under the shelf. "When gas is used the heater must be placed under- 

 neath the bath, where it is protected by the galvanized-iron box upon 

 which the bath rests. 



The thermometer is suspended through one of the holes in the top 

 of the bath by means of a perforated cork in such a way that it may 

 be read without opening the door. The temperature of the bath 

 should be kept at about 102° to 105° C. (215° to 221° F.). This tem- 

 perature may be readily controlled without any automatic device, as 

 the operator is usually working near the apparatus and can give it his 

 attention at any time. 



When only electricity is conveniently available, a small electric 

 heater may be used. The amount of heat may be controlled by means 

 of an adjustable resistance coil outside of the air-bath. This electric 

 heater has proved very satisfactory, and of course claims the advan- 

 tage of less danger of fire. Wherever gas is available, however, it 

 may be desirable to use it, as the heat thus obtained is rather cheaper 

 and is somewhat more easily regulated. 



The sieve used for determining the amount of broken material, dirt, 

 and other foreign matter is a plain metal sieve having 5 strands to 

 the inch. In other words, it is a wire screen having 25 square holes 

 per square inch. 



«An electric heater, with resistance coil, would cost about $11, bringing the total 

 estimated cost up to $67.15. 



