COOLING HOT-BOTTLED PASTEUEIZED MILK. 5 



The corrected anemometer readings were in every case higher by 

 approximately 10 per cent than those obtained with the Pitot tube. 



The wet-bulb and the dry-bulb temperatures were taken by a sling 

 psychrometer. The barometer was read during each test, and the 

 weight of air per cubic foot determined from the barometer and the 

 wet-bulb and the dry-bulb readings. 



Readings of air velocities were also taken with an anemometer over 

 the tops of the crates. These readings, taken at different places over 

 the stacks, were practically the same and averaged 182 feet a minute 

 over the quart crates and 156 over the pints. It is very important 

 that a practically uniform velocity of air be maintained throughout 

 the stack in order to cool all bottles at the same rate. Thirty crates, 

 stacked 5 high, were used in aU experiments, 15 for quart bottles and 

 15 for pints. Reading of volts, amperes, and speed of motor were 

 also taken during each experiment. 



RELATIVE RATE OF COOLING OF MILK AND WATER. 



As the average specific heat of whole milk is less than that of water, 

 it may be expected to cool faster under the same conditions. This, 

 however, is not the case when the cooling is done in bulk, such as when 

 in bottles or cans, as is plainly shown in figure 2. These curves are 

 plotted from temperature readmgs taken in a quart bottle of milk 

 and a quart bottle of water, subjected to the same conditions of air 

 velocity, air temperature, location of thermometers in bottles, etc. . 



It will be seen that the curve representing the rate of cooling the 

 mUk is of a uniformly higher temperature than the similar curve for 

 water. 



On account of the small variation in the relative rate of the cooling 

 of milk and water it was considered advisable to use water in these 

 experiments, as it was more easily obtained and handled. Bottles 

 of milk, however, were distributed throughout the crates, in selected 

 places, and hi these bottles, as well as m those containing water, simi- 

 larly placed, the temperature readings were taken. 



RELATIVE RATE OF COOLING WITH STILL AIR AND FORCED AIR. 



In order to obtain data to compare the rate of cooling bottles and 

 cans containing milk when exposed to still air and to moving air, pmt 

 and quart bottles, and 10-gallon cans of milk were placed in a refrig- 

 erated room, the constant temperature of which was held at approxi- 

 mately 40*^ F. (4.4° C). The initial temperature of the milk was 

 about the same in all instances. The results are seen in figures 3, 4, 

 and 5. Figures 3 and 4 show the relative drop in temperature between 

 pints and quarts, respectively, when exposed to still air and to mov- 

 ing air, and figure 5 shows similar results for the 10-gallon cans. 



