Tests for Jars and Rubbers
Jars should be tested before they are used. Some of the important tests are here given:
Glass-top Jars.—Fit top to jar. If top rocks when tapped it should not be used on that jar. The top bail should not be too tight nor too loose. If either too tight or too loose the bail should be taken off and bent until it goes into place with a light snap. All sharp edges on top and jar should be filed or scraped off.
Screw-top Jars.—Use only enameled, lacquered or vulcanized tops. Screw the top on tightly without the rubber. If thumb nail can be inserted between top and jar, the top is defective. If the edge is only slightly uneven it can be bent so that it is usable. Put on the rubber and screw on the top tightly, and then pull the rubber out. If the rubber returns to place the top does not fit properly and should not be used on that jar.
Rubbers.—Be very particular about the rubbers used. Buy new rubbers every year as they deteriorate from one season to another. It is always well to test rubbers when buying. A good rubber will return to its original size when stretched. When pinched it does not crease. It should fit the neck of the jar snugly, and be fairly wide and thick. It is cheaper to discard a doubtful rubber than to lose a jar of canned goods.