Small angle x‐ray scattering measurements are made on samples of colloidal gold of radius from 50 to 400 angstroms. Copper (1.54 angstrom wave‐length) and aluminum (8.32 angstrom wave‐length) radiation are used.The usual method of analysis is shown to be valid only for particles of radius less than 120 wave‐lengths. Extension of the method to larger particles is achieved, giving improved electron microscope correlation.The use of longer wave‐lengths and optimum shaped slits are shown to reduce geometry errors sufficiently to give clear evidence of predicted intensity maxima. The first three secondary shape function maxima are observed.An additional interference maximum attributable to particle‐to‐particle interference is observed. The position and magnitude of this maximum are correctly predicted by an expression based on earlier fluid scattering theory.