No. 4.] CANNING IN GLASS: 51 



kinds of glass jars, — the old and the new improved Mason jar 

 with a screw top, and the jar with a rubber ring and glass top, 

 of which there are several varieties. These tops are held in 

 place by a simple wire spring. Fruits, vegetables and meats 

 often spoil by the use of defective rings. It is poor economy 

 to buy cheap rubbers or to use them a second time. Let me 

 say right here that it is a good plan to test your rubbers 

 before using them, by pulling the rubber out and letting it 

 spring back into shape. If it does not respond readily you will 

 know it is not good. 



Another type of jar in common use is the one with the self- 

 sealing metal top lacquered on both sides. These jars require 

 no rubber rings, as the groove in the top contains a composition 

 of the consistency of rubber, which is melted during canning 

 by the heat of the jar. This band takes the place of a rubber 

 ring. 



If the jar and the food are not absolutely sterilized this jar 

 warns you of the fact by loosening its cap and unsealing itself. 

 This is due to the fact that the germs cause a gas to form 

 which loosens the cap. 



This type of jar seals itself by air pressure. When the food 

 in the jar is hot it is very much expanded, but in cooling 

 it shrinks and causes a vacuum. In shrinking it draws the cap 

 down tight, and by- atmospheric pressure (15 pounds to the 

 square inch) holds it tighter and tighter, until when cold it is 

 impossible to pull it off. 



Sterilizers. 



There are two principal types of sterilizers, — the first is the 

 hot water bath outfit, which consists of an ordinary wash 

 boiler with a rack that sets on the bottom to set your jars on 

 so as to avoid breakage; the other method is the steam pressure 

 canner. 



By using the latter sterilizer or canner your fruits are canned 

 by steam pressure instead of hot water. The food is cooked in 

 receptacles placed over water which is heated to a temperature 

 sufficient to make steam, and held there at that temperature 

 the required time. On the cover of the steam canner there is a 

 steam gauge, a safety valve and an exhaust cock. 



