Denver wonders if adding salt to water will make it boil at a lower temperature. What should he do next in order to follow the steps of inquiry?

In order to follow the steps of inquiry Denver should add some salt to water taken in vessel and heat it. Once the water comes to a boil, Denver should insert a thermometer into the boiling water and measure the temperature of it. Pure water boils at 100°C. Denver will have to note if the salt water boils at a higher or lower temperature than 100°C.