THE FRUIT JAR I97 



method (see page 200) this takes care of itself, as jar and 

 contents are sterilized together. In the open-kettle method it 

 is best to place the jar in cold water before filling, to bring 

 the water to a vigorous boil, and then to fill the jar while 

 still hot. Pouring boiling water into the jar is a simpler 

 method, but is not quite so certain. 



The glass fruit jar is almost universally used in the home, 

 is very convenient, and can be used again and again ; but in 

 canning factories the use of tin cans is largely adopted, since 

 they are less expensive and are to be used but once. The 

 principle of their use, however, is exactly the same as that of 

 the glass jar, although the details are different. The material 

 to be canned, with or without previous boiling, is put into 

 the tin can, upon which a cover is placed and sealed firmly, 

 the whole now being closed to the air except for a small 

 opening in the cover. Then the can, with its contents, is 

 placed in a convenient heating apparatus for thorough sterili- 

 zation. Open boiling or pressure heating is used, according 

 to the temperature desired ; in the former case the small 

 opening in the cover is not sealed until after heating, to 

 allow the escape of steam, while in the latter case the cans 

 are entirely sealed before processing. Cans are kept under 

 observation for a while to make sure that sterilization has 

 been complete, and any cans found to be swollen from the 

 accumulation of gas within are discarded as ruined. Canning 

 factories have sometimes suffered great financial loss from 

 the spoiling of their products, ordinarily because some highly 

 resistant spores have survived. Canners know to-day that 

 the remedy in such cases is the application of greater heat, 

 and thus are able now to avoid in great measure their losses 

 of previous years. 



