6 
BULLETIN 85, U. S. DEPARTMENT OF AGRICULTURE. 
regenerator varied from 29 f° to 83° F., an average of 53?° F. In 
other words, the milk arrived at the cooler 53 h ° F. lower in tempera- 
ture than it would have done had no regenerator been used. 
The regenerator is an efficient piece of apparatus when viewed 
from an engineering standpoint, but it has its disadvantages when 
viewed from the bacteriological standpoint, as it is difficult to keep 
absolutely clean and sterile unless given particular attention. 
DEPRECIATION OF DAIRY EQUD7MENT. 
Owing to the rough usage to which dairy apparatus is subjected, 
having to be taken apart for the purpose of thorough cleaning after 
each operation, and to the rapid development and improvement 
in this line of apparatus, it is assumed that about four years is its 
average useful life, at which time it is either worn out or antiquated 
and must be replaced. Therefore, it has been depreciated at the rate 
of 25 per cent per annum. 
The mechanical equipment (engine, boiler, shafting, etc.) necessary 
for the operation of the pasteurizing apparatus and which has been 
depreciated at the rate of 10 per cent per annum covers only that part 
of the total equipment which is used for pasteurizing. In other words, 
the total value of the mechanical equipment of the plant is prorated 
among the various processes through which market milk passes in a 
modern city milk plant. 
TESTS OF CREAM-PASTEURIZING APPARATUS. 
Tests made on the pasteurizing equipment in creameries covered 
both the flash and the holder processes. The pasteurizing was also 
accomplished by using (1) live steam direct from the boiler, (2) ex- 
haust steam from the engine or from steam-driven pumps, and (3) hot 
water heated by the exhaust steam from the steam-driven auxiliaries. 
In calculating the heat absorbed by the cream in the following tests, 
the specific heat of cream is taken as 0.90. In this connection it is 
well to state that there seems to be very little known at the present 
time concerning the specific heat of cream. It does, of course, van- 
to a certain extent with its chemical and physical composition. At 
a certain point on the temperature scale its specific heat is greatly 
increased, apparently above unity. This is attributed, however, to 
the melting of the butterfat and a part of the absorbed heat being used 
to effect the change. 
In Table 2 are given the results of tests on the pasteurizing equip- 
ment of four creameries. The tests were made under actual working 
conditions. In tests Nos. 1, 2, and 3 the pasteurizing was done by 
employing exhaust steam and in test Xo. 4 five steam was taken direct 
from the boiler through a reducing valve. 
