The properties of the solid conductivity state below 600° K are considered in the present Part. For comparative purposes the conductivity at 420° K is given the title of ‘low-temperature reference conductivity σ420’, and this function is studied in relation to its environment. It is found that σ420increases in almost linear fashion with increase of conditioning temperature and that it also increases with increase of chemical activity of the core metal. At constant temperature σ420is invariant over a wide range of applied voltage and current, and shows a high order of stability with time. Perhaps the most surprising result to emerge is the observed vulnerability of the solid conductivity to low-pressure oxygen attack, even at a temperature as low as 300° K.