Barnes worked with Callendar on extremely precise measurements in constant-flow calorimetry, in which a given amount of electrical energy is added to a given mass of flowing liquid whose consequent increase in temperature is precisely measured. Barnes pioneered the constant-flow calorimeter which is used by contemporary physical chemists. He also studied turbulence, electrolytes, and the heat effects of radium. In the 1920s, he became a world-class expert on anchor ice, frazil ice, and ice engineering.