24 BULLETIN 744, U. S. DEPARTMENT OF AGRICULTURE. 
In the northern section of the United States milk is frequently 
shipped to the city during the winter when the temperature of the 
air is below zero. Since milk freezes at a temperature between 
31° and 29° F., it is important that some provision be made to pre- 
vent freezing in transit. A test, therefore, was conducted to deter- 
mine the efficiency of the same cans used in the previous tests for 
preventing freezing. Because of the limited space in the refrigerator 
but two cans could be handled at a time. It was not possible to 
hold, therefore, all cans at exactly the same temperature during the 
test because of the difficulty in keeping the refrigerator at exactly 
the same temperature from day to day. The temperature of the re- 
frigerator ranged from 1° to 44° F., the average temperature being 
about 24 degrees above zero. The initial temperature of the milk, 
when the cans were placed in the refrigerator, was 77° F., and the cans 
were held until its temperature had reached 30° F. The drop in 
temperature is graphically shown in figure 18. Thetime required for 
the milk in the different types of cans to drop from 50° to 30° F. 
was as follows: 
Hours. Hours. 
Cat INO: di ond nat ee 20 |p Can Nos a2 Stet ee 163 
OEE ING) 52 Mites Sree lh er GE wth 3 io all a ral Can “No. 62: ) Sa ieee € 
GanUNo 4602 ba eke ee 2 ile le 183 | 
Can No. 3, the ice-compartment can, was not used as it was not 
suitable for the experiment. Comparing the time necessary for the 
temperature of the milk to drop from 50° to 30° F. with that of the 
ordinary can (No. 6) we find: 
Can No. 1 required 2.9 times as long. | Can No. 4 required 2.6 times as long. 
Can No. 2 required 3.0 times as long. | Can No. 5 required 2.3 times as long. 
The showing above indicates the efficiency of felt jackets or in- 
sulated cans for shipping milk in zero weather. 
TRANSPORTING MILK AT LOW TEMPERATURES. 
A large percentage of city milk supplies is delivered to the rail- 
road station by the producers or is brought to the station by wagons 
or trucks which collect milk from several farms. A certain quantity 
of milk is hauled directly to the city by means of teams or motor 
trucks. Unless the milk is especially protected its temperature will 
rise several degrees in the journey from the farm to the station, and 
if afterwards in the haul of from a few hours to all day to the city 
it is exposed to high temperatures its temperature when it reaches 
the market is usually not low enough to prevent the rapid multiplica- 
tion of bacteria. Much milk is transported to the city in ordinary 
baggage cars or in uniced milk cars. To insure its reaching the 
city in the best condition milk should be cooled on the farm to 50° 
F. or below and should be carefully protected during shipment to 
RSPR E> 
