The theory does go a long way in explaining the concept of heat, however, and it gives correct answers. Classical thermodynamics which governs our understanding of this is an equilibrium theory. Thus, we start from an initial state of two substances at equilibrium, place them in thermal contact and allow enough time so that equilibrium is established for the final state. This final state consists of the two substances in thermal equilibrium with each other and characterized by the same temperature. The final temperature of the two bodies depends on their initial temperatures and their heat capacities.
Temperature is that which is measured by a thermometer.
If we put a thermometer into a liter of water, allow equilibrium to be established , and record a reading and then take half of that liter we still obtain the same reading. Temperature is something apparently that does not depend on the amound of stuff we have. This is different than the idea of caloric, or more properly, heat. We can have more or less of it. The author in the reference cited below critizes this idea, but that author is not quite right.