  We have observed the dark cloud Barnard 68 with SCUBA at 850 um and with
SIMBA at 1.2 mm. The submillimetre and millimetre dust emission correlate well
with the extinction map of Alves, Lada and Lada (2001).The A_V/850um
correlation is clearly not linear and suggests lower temperatures for the dust
in the inner core of the cloud. Assuming a model for the temperature gradient,
we derive the cloud-averaged dust emissivities (normalised to the V-Band
extinction efficiency) at 850 um and 1.2 mm. We find k_850um/k_V = 4.0 +/- 1.0
x 10^-5 and k_1.2mm/k_V = 9.0 +/- 3.0 x 10^-6. These values are compared with
other determinations in this wavelength regime and with expectations for models
of diffuse dust and grain growth in dense clouds.
