PLUM MARMALADE [FROM AN OLD BOOK]

This recipe is from a book used by my great-grandmother. It was published in 1897, in Rio de Janeiro, then capital of Brazil.

Plum Marmalade
Peel very ripe plums and remove pits and skins from the inside. Weigh as much of plums as of sugar that you join and boil until marmalade consistence. Then crush four pits of the plums and join it to the marmalade. Four pits are enough for four pounds of marmalade. It is only to give the taste of the fruit.