COOLING, STORING, AND SHIPPING MILK. 21 



of ice into the tank and using a thermometer to ascertain the tem- 

 perature to which the milk is cooled. When milk is precooled by 

 means of a surface cooler to between 52° and 62° F. and is placed 

 in a cooling tank in which the temperature of the water is 45° F., 

 from 1^ to 2 pounds of ice for each gallon is necessary to cool milk 

 to and to keep it at 50° F. for a day. When precooling is not prac- 

 ticed and the tank water has a temperature of 45° F. about 4 pounds 

 of ice per gallon will be necessary. 



EFFICIENCY OF DIFFERENT TYPES OF CANS FOR HOLDING 



MILK. 



In order to determine the relative value of different types of milk 

 cans for maintaining low temperatures in milk held without agitation 

 for a considerable period, a series of experiments was conducted. Six 

 10-gallon cans were used, as follows : Nos. 1 and 2 were insulated ; No. 

 3 had an ice compartment ; No. 4 was an ordinary can covered with 

 1-inch felt jacket; No. 5 was an ordinary can covered with a ^-inch 

 jacket; and No. 6 was an ordinary milk can. The cans were placed 

 in a room in which the temperature was maintained at 74^° F. 

 The initial temperature of the milk in cans Nos. 1, 2, 3, and 4 was 

 35° F. ; in No. 5 it was 36° F., and in No. 6 it was 37° F.— The milk 

 was not stirred in any of the cans during the test, the temperature 

 reading being taken by removing the top and inserting a long- 

 stemmed thermometer into the center of the can. In each case for- 

 maldehyde enough was added to the milk to prevent premature 

 souring. 



The results of the test are shown in figure 16. It will be noted that 

 the time required for the temperature of the milk to rise to 50° F. 

 was as follows: 



Hours. 



Can No. 1 24 



Can No. 2 30 



Can No. 3 22 



Hours. 



Can No. 4 22 



Can No. 5 18 



Can No. 6 . 11 



It should be kept in mind of course that the initial temperature of 

 the milk in can No. 5 was 36° F. and in can No. 6 37° F. Comparing 

 the various cans with No. 6 (the bare, unprotected can) it will be 

 noted that No. 1 took 2.18 times as long; No. 2 required 2.73 times as 

 long; Nos. 3 and 4 required twice as long; and No. 5 required 1.63 

 times as long as No. 6 for the temperature of the milk to rise to 50° 

 F. The results indicate the efficiency of the various methods of pro- 

 tecting cans in keeping milk at low temperatures. 



In test No. 2 the conditions were similar to those in the first test 

 except that the room temperature was 99.5° F., or 25 degrees higher, 

 and the initial temperature of the milk in each can was 44° F. The 



