34 BULLETIN 880, U. S. DEPARTMENT OF AGRICULTURE. 
it is important that the boiler room be far enough away and so 
inclosed that dirt. soot, and fumes will not reach the milk-handling 
rooms. The power plant should be of ample capacity, so that none 
of the equipment or apparatus need be forced. It may be advisable 
for large plants to have two refrigerating machines and two boilers. 
Considerable power may be saved at certain times of the year by 
operating only one of the machines when the full capacity of refrig- 
eration is not needed. By having two boilers, one can be cleaned or 
repaired without shutting down the plant. 
STEAM OR ELECTRIC POWER. 
Whether a steam engine or electric motors should be used will 
depend largely upon the costs of current and coal. The use of motors 
has several advantages, and direct-connected motors for each ma- 
chine are advisable wherever possible, although where several ma- 
chines are grouped together less power will be required if only one 
motor is used to run the shafting for all the machines. At large 
plants electric current to run the motors can often be generated for 
much less than it can be bought. Some of the advantages of 
motors are : 
1. Simplicity of operation. 
2. Cleanliness. 
3. Power is nsed only when machine is operated. 
4. Small space required. 
5. Power used in operating a machine may be determined accurately at 
any time. 
6. Obviates insanitary hangers, shafting, and pulleys. 
Some of the advantages of the use of steam engines in milk 
plants are : 
1. The exhaust steam can be utilized. 
2. The source of power is under the control of the milk plant. 
3. A steam boiler must be used anyway to supply steam for hot water, 
pasteurizing, sterilizing, and for heating the building. 
Whatever power is used it is well to have an auxiliary system, so 
that if anything happens to one system the plant will not have to 
be shut down. A plant using motor power should have an engine for 
an emergency, while a plant using engine power should either have 
an extra engine or some electric motors installed. 
ARTIFICIAL REFRIGERATION". 
Most large plants use artificial refrigeration, but there are 
many smaller ones that still depend upon ice. Individual condi- 
tions will determine which will be more economical to use. 
The methods of producing artificial refrigeration are familiar 
to most milk dealers. They are fully described in United States De- 
partment of Agriculture Bulletin 98. 
