The problem of the changes in structure and physical properties which occur when alloys melt is discussed. From a review of published data on this subject, it is concluded that the inter-atomic forces which give rise to compound formation in the solid state are also satisfied in the disordered liquid structure. Suggestions are made for the systematic examination of a series of magnesium alloys to determine the effect of the electrochemical factor on the physical properties of liquid alloys. (L.T.W.)