A differential microcalorimeter of the Tian‐Calvet type has been designed and constructed. The galvanometers previously employed have been replaced by a dc amplifier, which materially simplified the construction and operation of the instrument. In addition, this allows an electrical analog integrator to be used which gives directly the heat of reaction. Sensitivity of the instrument in the range from 0.01 to 2 cal is such that measurements can be made with a precision of 1% or better. Measurements have been made, under ideal conditions, of 0.002 cal with a standard deviation of 0.1%.