How do you know that a sealed calorimeter is a closed system? because the temperature is conserved because the masses of the sample and water are equal because the thermal energy is not transferred to the environment because the work is done on the test sample

A sealed calorimeter is a closed system because thermal energy is not transferred to the environment.

A closed system is an isolated system where there is no transfer of energy with its surroundings. Also the system is not subjected to any external force whose source is external to the system.

.) the observation by semmelweis that more mothers died of childbed fever when their doctors also worked in the morgue