j 
} 
/ 
80. BULLETIN 1022, U. S. DEPARTMENT OF AGRICULTURE. 
-The outstanding feature of these curves is the fact that by far 
the greatest reduction in pressure during the 45-minute process period 
occurred as the result of the first two minutes of the exhaust. Inthe — 
case of the No. 2 can this was a reduction of about 7 to 8 pounds 
per square inch during the first two minutes, which was lowered 
~ only about 1.8 pounds further by a 6-minute exhaust. The curves. 
for the No. 3 can show the same thing, except that the maximum 
pressure developed in the can not exhausted was not so great. It 
is obvious that. the temperature of the head space is the greatest 
factor in determining the vacuum and pressure, for the average of 
the can at the end of two minutes could not be high enough to account 
for the low pressure and high vacuum thus obtained. The effective- 
ness of a short exhaust, as in the case of peas, would be realized only 
by immediately sealing, as will be shown later by the results of 
vacuum tests on cans in lots which were exhausted in the steam 
box for the different exhaust periods and then removed and sealed at 
once. 
VACUUM STUDIES. 
The figures for the vacuum obtained in the cans used in the pres- 
_ sure tests which are of interest are presented in Table 8: 
TABLE S—Vacuwuim tests with tomatoes in No. 2 and No. 3 tin cans. 
| Temperature (°C.).| Time (minutes). | Barometer reading. 
: ’ inches 
Sr en Material | atter | psnanst(Lengthof| At Alter ahpolnee 
= at ’ cooling. ‘| process. | sealing. | cooling. HEY) 
24 163 2 45 29. 85 29. 80 15 
NOS2 3s. Bee et re eel 234 alg 4 45 29. 80 29. 7. 163 
23 19 6 45 29. 39 29. 39 173 
: 254 222 2 “45 29. 86 29. 85 15 
NOs 3 Se ee ee eee 20 22 4 45 29. 80 29. 80 15 
| 24 213 6 45 29. 73 29. 39 16 
With the increase in exhaust there is shght increase in vacuum, 
which corresponds well with the figures on pressures, and they are 
found to be fairly high. ; 
The average vacuum readings upon No. 3 cans in lots, exhausted 
for different periods in the steam box and then sealed in the mechani- 
cal sealing machine, were as follows: 
i-minute . exhaust22=-? = Pra LEAS ee ig Se _ 3 inches. 
2-mintte\exharshe so ey aoe ae te a eee 4 inches. 
3-Minute exhaust: 2 2)\o2 sat ey 2 ieee ee 4 inches. 
4-minnte, exhaust)... f- 5.16 Rocke eee er eee 64 inches. 
5-minute exhaust 2.22 ae 5 ae ee eee ee ae eee 8 inches. 
It is seen that these values are considerably below those in which 
the cans were sealed while still in the retort, and they illustrate how 
