  We present results of a study of the soft X-ray excess in the black hole
candidate Cygnus X-1 made with the {\it Rosat PSPC}, using observations taken
during persistent emission at orbital phases close to 0.5. The soft excess can
be well fitted as a blackbody with temperature $\rm {kT_{bb}}$ = $\rm {0.13\pm
0.02}$ keV. $\rm {kT_{bb}}$ did not vary appreciably with intensity of the
source. By assuming that the distance of the source is its lower limit of 2.5
kpc, a luminosity of the soft excess of $\rm {4.7\cdot 10^{36}}$ erg $\rm
{s^{-1}}$ was obtained. From this, disc temperatures were calculated as a
function of radius, assuming the compact object to be a 10 $\rm{M_{\sun}}$
black hole, in particular, the temperature at 7 Schwarzschild radii expected to
be highly representative of the total disc emission. This was found to be 0.13
keV, in very good agreement with the spectral fitting result. This good
agreement strongly supports the identification of the soft excess with emission
from the disc around a black hole.
