This section is from the book "Save It For Winter.", by Frederick Fry Rockwell. Also available from Amazon: Save It For Winter; Modern Methods Of Canning, Dehydrating, Preserving And Storing Vegetables And Fruit For Winter Use, With Comments On The Best ... For Saving, And When And How To Grow Them.
The grooves around the tops of the filled cans are wiped to clean them from juice and pieces of fruit, and the caps applied. A brush dipped in solder fiux is then passed around the groove. The capping steel, heated until it will melt solder instantly, is cleaned by dipping in solder flux and applied immediately to the groove of the can. If plain caps are used, a little solder is melted around the bottom of the steel and allowed to run into the groove. Only a little is necessary. If solder-hemmed caps are used, no other solder is needed. The steel is turned a few times to distribute the melted solder evenly in the groove and then slightly raised while pressing down on the center rod for an instant until the solder hardens.
Fig. 42 - Getting ready to seal tin cans. The soldering iron must be coated with tin. a - flux jar and brush for applying same; b - solder-hemmed cap or top for can; c - bar sal ammoniac; d - soldering iron (for tipping copper); e - roll of wire solder.
Fig. 43 - First step in sealing can; applying the liquid flux to rim of can. a - capping iron; b - head of inner steel, working in handle; c - applying flux to rim of cap; d - soldering iron.
Fig. 44 - Sealing a solder top can. 1. Wipe the juice and syrup from the groove. 2. Apply cap and wipe the groove with a brush dipped in soldering fluid. 3. Place clean hot capping steel on can and melt a little solder into groove. 4. Turn the top steel to distribute the solder. 5. Press down on center rod, and raise steel a few seconds to allow solder to harden. 6. After exhausting can wipe vent hole and seal with a drop of solder.
This term means the closing of the small vent hole in the top of the can with a drop of solder. It is done while the contents are hot and before sterilizing. The edges of the holes are cleaned with a brush dipped in solder flux. Very little must be used or it will run onto the can and injure the contents. After applying the flux, the properly tinned and heated tipping steel is applied to the hole and touched with a piece of wire solder. This causes a small piece of melted solder to run to the point where it closes the hole and is smoothed with a quick twist of the steel.
This process is necessary with nearly all air-tight containers which are to be sterilized by heat. It consists of a preliminary heating before sealing and be fore the final sterilization. It results in expanding the air inside the container and thus driving out most of it. when the sealed container and its contents cool, the small amount of air still enclosed contracts and produces a partial vacuum. If cans are sealed while the contents are cool they will swell on heating, owing to the expansion of the heated air. Exhaustion is also necessary with jars. If the covers are screwed or clamped on, the expanding air may break the glass. If they simply rest on the rubber or other sealing ring, the vacuum is necessary to keep them in place.
If the fruit is hot when placed in the cans or jars they may be sealed and sterilized immediately as the heat will exhaust the air sufficiently.
For the sanitary cans, full instructions are sent with the different machines made for the sealing or clamping on of the covers.
Fig. 45 - Sealing-machine for mechanically sealed or "sanitary" tin cans; especially good for Canning Clubs, Granges, and so forth.