While all of this is very nice you should note that the font
used to set the chapter number does not change with the text.
This illustrates something about TEX's grouping symbols.
Since we put the control sequences for changing fonts inside the
braces, only the text inside the braces is affected.
That is, the change only occurs locally.
In general any change you make inside a pair of curly braces only
affects the material inside the braces, unless you force
the effect to persist.
(If you want to know how to do this look up the
global
command in the TEX book.)
It follows, therefore, that if we want the number to change
we have to change the font before we give the
chapter
command.
If you type =by -1
{
bf
chapter{ Formatting Text}}
you get