46. For canning food in some tin cans, it is necessary to have a
soldering outfit for properly closing them. This consists of a capping
steel, a tipping iron, solder in small strips and in powder form, a
small can of sal ammoniac, and a bottle of flux, which is a fluid that
makes solder stick to tin.
47. Prepare the food that is to be canned in tin cans in the same way as
for canning in jars by the cold-pack method; likewise, pack the cans in
the same way, but allow the liquid and fruit or vegetables to come to
within only 1/4 inch of the top. Then proceed to close the cans. Apply
the flux to the groove in the top of each can where the solder is to be
melted, using for this purpose a small brush or a small stick having a
piece of cloth wrapped around one end. Heat the capping steel, which
should be thoroughly clean, until it is almost red hot, dip it quickly
into a little of the flux, and then put it into a mixture consisting of
equal parts of sal ammoniac and powdered solder until it is covered with
bright solder. Put the cap on the can and apply the hot capping steel
covered with the solder. Hold this device firmly, press it downwards,
and turn it slowly as the solder melts and thus joins the cap to
the can.
48. After the caps are soldered in place, the air inside the cans must
be driven out through the small vent, or opening, usually in the center
of the cap, and the cans made air-tight. Therefore, place the cans into
boiling water to within 1/2 inch of the top and let them remain there
for a few minutes. Usually, 3 minutes in boiling water is sufficient.
Immediately after _exhausting_, as this process is called, apply a
little of the flux as in capping, and, with the tipping iron well heated
and a strip of solder, seal the hole in the caps. After this is done,
test each can for leaks by submerging it in water. If bubbles arise, it
is an indication that the cover is not tight and must be resoldered.
49. The next step consists in processing the cans of food. This may be
done either in a water bath or in a pressure cooker. If the cans are to
be processed in a water bath, keep them in the boiling water just as
long as glass jars of food would be kept there. If a pressure cooker is
to be used, keep the cans in it for 6 to 40 minutes, depending on the
steam pressure employed, the ripeness of the food or the necessity for
cooking it, and the size of the cans employed. For canning meat or fish,
processing in a pressure cooker is the most successful, as the high
temperature reached in it kills bacteria, which are difficult to destroy
at the boiling point.
As soon as the cans of food are removed from the water bath or the
pressure cooker, plunge them into cold water to stop the cooking and
prevent the food from getting soft and mushy. Then label the cans, so
that no mistake will be made as to their contents.
50. In another method, the tin cans may be closed without soldering the
caps on. The caps used in this case are different from those which must
be soldered. They are forced in place by a hand-pressure machine that
may be attached to a table. Otherwise the procedure is the same as that
just given.