Diffusion coefficients for the ammonium ion were obtained at 15-45 degrees C by nuclear magnetic resonance (N-15-NMR) spin-echo techniques in 72 and 86 wt% aqueous ammonium chloride 98% enriched with N-15. Diffusion coefficients for succinonitrile and water in a 9.4wt% aqueous mixture (25-45 degrees C) and for succinonitrile and acetone (35-55 degrees C) in a mixture with 8.8 wt% acetone were obtained similarly with H-1-NMR. The coefficients were compared with those from earlier studies of these systems, which are models for the solidification of metals.