The melt viscosities for , , and as a function of temperature to 950°C have been precisely determined. The temperature dependence of the viscosities can be expressed by the Arrhenius‐type equation: , the values for and E(kcal mole−1) being respectively: , 141, 16.9; , 4.9, 25.7; , 1.35, 29.1. The experimental values for correspond closely to those predicted theoretically for the transport process, assuming that viscous flow is primarily controlled by migration of the carbonate ion in these melts. Electrical transport and viscous flow in carbonate and chloride melts are briefly examined.