UNITED STATES DEPARTMENT OF AGRICULTURE 
Contribution from the Bureau of Animal Industry 
JOHN R. MOHLER, Chief. 
Washington, D. C. PROFESSIONAL PAPER January 17, 1919 
COOLING MILK AND STORING AND SHIPPING 
IT AT LOW TEMPERATURES. 
By JAMES A. GAMBLE, Market Milk Specialist, and JoHN T. BOWEN, 
Technologist, Dairy Division. 
CONTENTS. 
Page. Page 
Scope of experimental work.........-.------ - 1 | The construction of milk tanks.............. 15 
Giteyprincipl eon cookin gases eee eee he 15 Mow vorcoolmullkqiickiliy 332 Pepe ee eee 18 
Coolingwmill< onthe farm).= 22. 222-..--222..- 4 | Efficiency of different kinds of cans for hold- 
Effect of low temperatures on bacterial count ENP oe ea cece cic Siew cere eae ter 21 
OTe ee ae a oS ele 4 | Transporting milk at low temperatures... 24 
Cooling efficiency of various kinds of tanks... Pil Mts blobsa A Ree ae ON oO OAs oSea se eUler 28 
SCOPE OF EXPERIMENTAL WORK. 
The experimental work reported in this bulletin covers (1) the 
relative efficiency of cooling tanks of different construction handled 
under varying conditions; (2) the most efficient methods of cooling 
and storing milk on the farm; and (3) the transportation of milk 
at low temperatures to market. 
THE PRINCIPLE OF COOLING. 
If a warm body is placed in contact with a cold one, heat will flow 
from the warmer to the colder until both have reached the same 
temperature. The rate of this flow depends upon the difference of 
temperature between the two bodies. Heat flows most rapidly when 
there is the greatest difference in temperature, and the rate grad- 
ually decreases as the temperatures become equal. 
The temperature of a body does not give a true indication of the 
amount of heat it contains. Heat is commonly measured by a unit 
called the British thermal unit, usually abbreviated B. t. u., which is 
the heat necessary to raise the temperature of 1 pound of water 1° F. 
The reason that the heat required to raise 1 pound of water 1° F. is 
taken as the unit is because water is one of the most difficult of all 
substances to heat. Practically all other substances require less heat 
to raise a unit quantity 1° F. For example, the heat necessary to 
raise 10 pounds of iron 100° F. is only 10 X 0.113 & 100 = 113 B. t. u. 
In other words, while it takes 1 B. t. u. to raise 1 pound of water 
81238°—Bull. 744191 (1) 
