I have had this piece of silver for some time (a family piece). There are no hallmarks on it but I think it is silver. It is inscribed with the words Quand vous avez froid pensez a moi.
It has a hinged handle at the top and the lid screws off. I took it to a silver dealer but he had not seen one of these before and was not sure what it was. It is rounded on the back as well as the front and is very tactile. It is about 3.5 inches tall excluding handle and around 8 inches in circumference.