16 



BULLETIN 1022, U. S. DEPARTMENT OF AGRICULTURE. 



Table 4. — Increase in the volume of water in No. 2 and No. 3 tin cans when 

 processed at different temperatures, the initial volume in No. 2 cans being 550 

 c. c. and in No. 3 cans, 950 c. c. 



[Based on Smithsonian tables.] 





Temperatures (° C). 







Volume (c. c). 







No. 2 



cans.- 



No. 3 cans. 



Sealing. 



Process- 

 ing. 



Total. 



Increase. 



Total. 



Increase. 



20 



t 100 

 I 110 

 1 115.5 

 I 121.1 



f 100 

 110 

 i 115.5 

 I 121. 1 



f 100 

 110 

 i 115.5 

 I 121.1 



572.8 



577.2 

 579.7 

 585.3 



561.1 



565.4 

 567.9 

 673.3 



557.7 

 562.0 

 564.4 

 569.8 



22.8 

 27.2 

 29.7 

 35.3 



11.1 

 15.4 

 17.4 

 23.3 



7.7 

 12.0 

 14.4 

 19.8 



989.4 



997.0 



1, 001. 3 



1,010.9 



969.2 

 976.7 

 984.9 

 990.3 



963.3 



970.8 

 974.9 

 984.2 



39.4 

 47.0 



70 



80 





51.3 

 60.9 



19.2 

 26.7 

 34.9 

 40.3 



13.3 

 20.8 





24.9 

 34.2 



Relation of barometric pressure. — A factor of considerable impor- 

 tance concerned with vacuum in cans is the barometric pressure, 

 especially as related to differences in altitude. Table 5 shows the 

 differences in barometric pressure for altitudes ranging from sea 

 level to approximately 6,000 feet and how, for example, food ma- 

 terials packed at or near sea level would lose in vacuum by over 3 

 inches, under identical temperature conditions, when shipped to a 

 place 3,000 feet above sea level. This loss would be increased, of 

 course, if those shipments were made to hot climates or during the 

 summer. 



Table 5. — Barometric pressure for different altitudes. 



[Taken from Smithsonian Meteorological Tables, 4th rev. ed., 1918, pp. 136-137.] 



Altitude. 



(sea level) . . . 



100 feet 



210 feet 



302feet 



403feet 



505 feet 



Baro- 

 metric 

 pres- 

 sure. 



29.90 

 29.79 

 29.68 

 29.57 

 29.46 

 29.35 



Altitude. 



1 

 Baro- 

 metric 

 pres- 

 sure. 



607feet 



29.24 

 29.14 

 29. 03 

 28.92 

 28.82 



700feet 



803feet 



906feet 



1,000 feet 





Baro- 



Altitude. 



metric 





pres- 





sure. 



1,504 feet 



28.29 



1,999 feet 



27.78 



2,502 feet 



27.27 



3,005 feet 



26.77 



3,497 feet 



26.29 



Altitude. 



3,998 feet 

 4,49Sfeet 

 5,006 feet 

 5,503 feet 

 5,997 feet 



Baro- 

 metric 

 pres- 

 sure. 



25.81 

 25.34 

 24.80 

 24.42 

 23.98 



While these matters may not be of great importance it is probable 

 that the unfortunate experience of some canners has been due to some 

 of these factors or to a combination of them. 



VACUUM STUDIES. 



Vacuum readings obtained in tests. — To determine how closely ex- 

 perimental results with tin cans would agree with the theoretical 



