Continuous Process [VAPORATORS 173 
Speed of Agitator.—The proper speed of the continuous 
concentrator is expressed in terms of rim speed, that is the 
distance which the blades travel per minute. It has been found 
that the rim speed which is sufficient ta move the film of milk 
in the machine properly, 1s about 2500 feet per minute. In order 
to insure a rim speed of 2500 feet per minute, the blades in a 3 
‘ 2500 aes 
foot diaineter machine must revolve ————= 265 times per 
3x3.14 
minute. Ina six foot diameter wheel, the same rim speed would 
2500 oe ; : : 
require ———— = 133 revolutions per minute of the spider. 
6x3.14 
Again, it has been found that the blades should be not more 
than about 24 feet apart. A three foot diameter concentrator, 
therefore, requires four blades while concentrators with larger 
diameter require a larger number of blades in order to keep the 
distance between blades within the limit of two and one-half 
teet. 
Operation of Continuous Concentrator.—The operation of 
the continuous concentrator is simple and the ratio of concen- 
tration of the product can be regulated as desired. 
Heating of Milk.—-Similar as in case of evaporation in 
vacuo, it is desirable, if not necessary, to heat the milk before 
it enters the concentrator. This not only increases the capacity 
of the machine, but it also prepares the casein in the milk for 
the superheating to which the milk is subjected in the concen- 
trator. Any method of forewarming or preheating may be used 
for this purpose. but since the milk flows to and through the 
concentrator, in a continuous stream, it is preferable to also use 
a forewarmer of the continuous type. The milk should be heated 
to about 185 to 200 degrees F. and the forewarming should be 
so arranged that the milk is exposed to this temperature for 5 
to 10 minutes before it enters the concentrator. 
Condensing.—The concentrator is steamed, the parts of the 
agitator are assembled and installed in their proper place, the 
cover is securely bolted over the opening in the front head and 
the machine is ready for operation. Before starting the agitator 
a small amount of milk 1s permitted to flow into the concentrator 
