  Using a new technique we have determined a value for the constant of
proportionality between submillimetre emission and dust mass, the dust mass
absorption coefficient at 850 microns. Our method has an advantage over
previous methods in that we avoid assumptions about the properties of dust in
the interstellar medium. Our only assumption is that the fraction of metals
incorporated in the dust is a universal constant. To implement our method we
require objects that have submillimetre and far-infrared flux measurements as
well as gas mass and metallicity estimates. We present data for all the
galaxies with suitable measurements, including new submillimetre maps for five
galaxies. We find kappa(850 microns)=0.07 m^2/kg
