May, 1929] FOODS IN A COLLEGE COMMUNITY 11 



a previously weighed dish or pan.i The pan and contents are then 

 placed either in an ordinary "air-bath" or in an electrically heated 

 oven. It so happened that throughout most of this research an elec- 

 tric oven was used having four heating units, which made it possible 

 to adjust the temperature at from 50° to 80° or 90° C. The many 

 shelves in the oven permitted changing positions of the dishes, so 

 that the samples were dried rapidly and in sequence. The drying 

 usually requires from 24 to 96 hours, depending upon the water con- 

 tent and, to a certain extent, upon the fat content of the sample. 

 Frequent stirring, especially of watery and fatty food, either with a 

 glass rod (weighed with the pan) or with a knife which can be 

 scraped clean upon the side of the pan, is necessary, since the top 

 of the sample sometimes dries and forms a hard crust, while the 

 bottom remains moist and is apt to mold, unless thoroughly dried. 



When the sample has reached a seeming dryness, the pan is taken 

 from the oven, placed on a shelf in the laboratory, and left for a day 

 or two so that the dried and thoroughly stiiTed sample may adjust 

 itself to the humidity of the air. The pan with its contents is then 

 weighed again, and the difference between this weight and the initial 

 weight of the empty pan represents the air-dry weight of the sub- 

 stance. The sample is now dry enough to burn, but may need to be 

 put, first, through a grinder or chopping machine. Two or two and 

 one-half grams of the air-dry, ground substance are weighed into 

 each crucible, ready for combustion. This amount permits good 

 sampling without too great comminution. 



Samples of salads which cannot be made homogeneous by mixing, 

 because of the large amount of oil in the mayonnaise, may be dried 

 with known weights of bread or cracker meal of known caloric value, 

 or a small amount of powdered pumice stone may be added to the 

 sample. Powdered pumice stone may also be mixed with or spread on 

 top of carbohydrates before burning, to keep them from frothing over 

 the edge of the crucible, but this, we find, is not necessary with 

 small samples of cane sugar. During the burning of some sub- 

 stances, such as salads, sandwiches, or doughnuts, soot will be de- 

 posited on the chimney or unburned carbon will be left in the cru- 

 cible, if the combustion is not regulated. Pumice stone mixed with 

 the sample after weighing will retard the combustion so that the 

 flame does not touch the chimney, but the oil or fat is apt to soak 

 through the pumice stone to the bottom of the crucible and not burn. 

 To avoid this, the food sample arid the pumice stone may be mixed 

 with a glass stirring rod and the mixture allowed to remain in a lump 



(1) In the case of the meals incUiding more than one food, the servings 

 were added one at a time to the pan and the pan and contents weighed 

 after each addition, each gain in weight representing tlie fresh weight of 

 the particular item added to the pan. 



