Why is the letter F used instead of S in Old-Fashioned Spellings?
In genuine old-style printing, it is not the letter f, but a long form of the letter s (derived from handwriting styles) which looks very similar to f but does not have a complete cross-bar. It is not used at the ends of words and in double s it is sometimes paired with a short s (which results in a compound letter like the German double-s (or sz or symbol ß). It fell out of fashion with printers rather suddenly in about 1780.