In the metallic arc welding, the welding rod, as well as the welder and welding operator, is one of the most important factors on which success of the welding depends. But the rod is directly and greatly influenced by the welding flux with which it is coated.<BR>The writers made an investigation of the effects of welding fluxes on the characteristics of the electric arc, using about 30 kinds of ordinary compounds The result is summarized as follows:<BR>(i) When a metallic oxide was used as welding flux, there was observed a definite relation of the atomic weight of the metal to the arc voltage and melting ratio, which varied according to the group of<BR>metals as established by the periodic law.(ii) There was a definite relation between the arc voltage and melting ratio irrespective of the property of the welding flux.<BR>(iii) Some kinds of welding flux caused a great difference between the values of the arc voltage and melting ratio obtained by connecting the welding rod with the anode and those obtained by connecting it with the cathode.<BR>(iv) The arc voltage and melting ratio varied according to the chemical composition and physical property of the welding rods. When the rods were coated with a definite kind of welding flux, however, the arc voltage and melting ratio had values which were dependent upon the flux.<BR>Any welding flux which was applied separately showed a definite arc voltage, which was dependent upon its polarity, The value of arc voltage, varying only with the flux, was quite free from the influences of the properties of the welding rod, amount of arc current, thickness of the coating of flux, etc, and was a factor having the greatest effect on the characteristics of the welding arc. This is a specially noticeable fact which has been confirmed by the experiment.