14 BULLETIN 1022, U. S. DEPARTMENT OF AGRICULTURE. 
final result. This finding is entirely at variance with the statement 
of Bitting and Bitting (7, p. 27) that when the container is en- 
tirely filled the pressure is greatly increased. 
The explanation of the decrease of maximum pressure with devemee 
of head space is found by a glance at the tables on the distortion of 
cans and the expansion of water and the theoretical curves of figure 3. 
= comparison of the expansion of water with the cubical expansion 
of the can (Tables 1 and 2) it will be seen that the distortion of the 
can under pressure is always greater than the expansion of water, 
which results in the creation of a greater head space. Consequently, 
the ratio between the head space and the distortion of the can is 
greater the smaller the head space, and therefore with decrease in 
head space a slight decrease in maximum pressure is to be expected. 
The greater distortion of the larger can accounts for the eee 
variation from the theoretical. 
Distortion of can and increase in volume.—Every change in pres- 
sure causes more or less distortion of the can, which alters its cubical 
contents. How great this distortion actually is is shown by Table 2 
which gives the experimental findings on the increase in volume in 
No. 2 and No. 3 tin cans when subjected to various internal pres- 
sures. These figures present the averages of a number of tests. | 
TABLE 2.—Increase in volume of No. 2 and No. 3 tin cans as the-result of dis- 
tortion caused by internal pressures. 
|! 
Increase in volume : gee in volume 
ese pe 
Pressure per square inch in|__——(—C—CCCC || Pressure per square inch in 
can. can. 
No. 2 No.3 || No. 2 No.3 
cans cans. | cans cans 
24 POHNGS 22 os5- 223 ae see 5.4 28.3.|| 20 pounds220 se Seer ieee 26.5 65.6 
5 pouUndSasess = ee ee ee 42.1 Sie dell ZopOunGS. eases ee peas 31.2 76.9 
10 pounds23 2.5 tes 18.0 46.0 1) S0(pounds2 222) 3-2 G25 sie & Obrip | ee 
WopOUNGS = sce sarees cee neces 22.6 54.6 | 
; i 
It will be seen that within the range of canning operations the 
cubical content of cans may be increased up to. 5 per cent or more, 
depending somewhat upon the size and strength of the individual 
cans used. 
The increase in volume due to distortion of the can-explains the 
decrease in pressure, and since this distortion increases with the 
higher temperatures greater variations from the theoretical must take 
place. Inasmuch ‘as sealing at the higher temperatures causes less 
strain on the can and consequently less distortion when subsequently 
processed, the theoretical values are more closely approached. 
