Excellent question! (and one I often get when posting older printed items)
It’s actually not an f, it’s an ſ or
“long s”. The ‘long s’ was used alongside the ‘round s’ (the modern lower case s) until the early 19th century, and is one of several letter forms and “ligatures” which have fallen out of use in modern English.
Generally speaking the long s was used at the beginning and in the middle of words, and as the first s when two s’s occurred in a row. You very rarely see a long s used at the end of a word.
In its printed form the long s does look very much like an f, but either doesn’t have have a cross bar, or only has it on one side. Or at least it’s supposed to, but very often printers would just use the two interchangeably which can get very confusing.
Here’s a printed style long s in the word “Congress” from the beginning of the Bill of Rights…
In its common handwritten form the long s is much more “loopy” and easier to distinguish.
Here are two handwritten long s’s from the Declaration of Independence.
You can see how when two s’s are used together the first one is “long” and the second one is “round”.
I found the whole long s thing weird and impractical UNTIL I actually tried writing a document in 18th century style cursive and suddenly the skies opened up and it made perfect sense. The long s is SO much easier to write than our modern round s, especially when there are two s’s in a row.
I, who am an old fogey who still writes in cursive, will fully admit that the long s has inadvertently ended up sneaking its way into my daily handwriting, especially when I’m taking notes.
The long s can be confusing when you first start out reading old books and documents, but if you keep at it I promise you will get to a point where you don’t even consciously notice it anymore.
