  A classic sum rule by Das et al. is extended to seven of the low-energy
constants $K_i$, introduced by Urech, which parameterize electromagnetic
corrections at chiral order $O(e^2p^2)$. Using the spurion formalism, a simple
convolution representation is shown to hold and the structure in terms of the
chiral renormalization scale, the QCD renormalization scale and the QED gauge
parameter is displayed. The role of the resonances is studied as providing
rational interpolants to relevant QCD n-point functions in the euclidian
domain. A variety of asymptotic constraints must be implemented which have
phenomenological consequences. A current assumption concerning the dominance of
the lowest-lying resonances is shown clearly to fail in some cases.
