Traditional reaction calorimeters require highly trained operators and the use of a large sample size (10 ml to 1000 ml) which is incompatible with highly reactive substances. A new calorimeter with a 2 ml or less sample size lends itself to the determination of reactivity of materials for process safety and to the determination of safety of materials shipped in compartment tank cars. The TC-100 Titration Calorimeter meets these requirements. A cost effective instrumentation of a differential cell design provides high sensitivity heat flow measurements. Automatic liquid injection and continuous mixing provides information on the heat of reaction and its rate. A portable instrument with small sample size allows for rapid temperature equilibration and safe handling of very reactive materials.