This section is from the book "Facts Worth Knowing", by Robert Kemp Philip. Also available from Amazon: Inquire Within for Anything You Want to Know.
Cut out a piece of tinfoil the size of the surfaces to be soldered. Then dip a feather in a solution of sal ammoniac, and wet over the surfaces of the metal, then place them in their proper position with the tinfoil between. Put it so arranged on a piece of iron hot enough to melt the foil. When cold they will be found firmly soldered together.
 
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