The stability of the iron welding arc is influenced by a number of factors, such as the nature and the aerodynamic state of the surrounding atmosphere, the strength and distribution of the magnetic field, the composition of the electrode, the nature and the amount of gases occluded in the electrode, etc. In this paper, however, only the first item has been discussed in an attempt to show that the cooling of the electrode and the arc core by dissociation of the surrounding gas has the preponderent influence on the stability of the arc.