Measurements were made of the heat released during decay of the afterglow, the viscosity, and the free electron density in active nitrogen. Calorimeter measurements of the heat released during decay of the afterglow amounted to as much as 22.3 calories per gram of the gas, corresponding to an excitation of one part in 350 of the molecules present to an energy of 9.6 electron volts. The viscosity of the active nitrogen was found to be the same as that of the unactivated nitrogen within one‐half of one percent. Ionization in a stream of active nitrogen is shown to be incidental rather than essential to the production of the Lewis‐Rayleigh afterglow. Microwave measurements of the free electron density in a stream of active nitrogen indicated one free electron for each 2.3×108molecules in the stream. Contrary to Mitra's theory, probes in the stream were found to respond to carriers of negative sign rather than positive ions. Space discharges in an expanding stream of active nitrogen are attributed to free electrons moving with the stream. In the use of active nitrogen for studies of low density flow, by observation of the afterglow, disturbing effects will occur because of heating and ionization, but the disturbances appear not to be so large as to interfere with its use.