Convert from firkin [butter, soap] to quintal [French]

Unit Definition (firkin [butter, soap])
The firkin [butter, soap] is a traditional unit of weight for butter and soap, equal to 4 stone or 56 pounds (about 25.40 kilograms).

Unit Definition (quintal [French])
The quintal [French] is a traditional unit of weight in France. The traditional French quintal equaled 100 livres (48.95 kilograms or 107.9 pounds), but today the word "quintal" in France usually means a larger metric unit.