I'd wager it is derived from Flemish.Algot Runeman wrote:ampersand
late 18th century: alteration of and per se and '& by itself is and', chanted as an aid to learning the sign.
In bygone days a thin dusting of fine white sand was sprinkled around the Louvain-type stove, and hawking salesmen with pushcarts travelled the streets, loudly yelling "Moet-er-geen-zand-zijn?" (No need of sand?).
If my greatgrandmama were still alive, she would unhesitatingly confirm it. (grandma's house had coal-fueled central heating and a gas range)
Flemish people with limited means had to use the expensive white sand very sparingly. Those people with very little sand in their kitchen had "amper zand" (barely sand) available, hence "ampersand" designated poor families.
"Amper" is also used in Suid Afrikaans, as in:
"Amperbroekie", meaning "barely there panties"