New constraints on composition-dependent interactions weaker than gravity

Results from two recent ``fifth-force'' experiments disagree when analyzed in terms of a single baryonic interaction. We consider an interaction coupling to q₅=B cosθ₅+L sinθ₅ where θ₅ has a value that could explain our null Cu-Be data while preserving Thieberger's positive Cu-H₂O result. (B and L are baryon and lepton number, respectively.) We present new Al-Be data that rule out this possibility except for a narrow region around θ₅{}-63^∘{} (q₅{∝}I₃, the third component of isospin), where the q₅ of terrestrial sources vanishes.