Colloidal Gold and Gelatin. A mixture of Auqo (0.0005
per cent Au) and gelatin (0.01 per cent), was placed in
the ultraapparatus. The activity of the gold particles
had somewhat diminished, everything else being appar-
ently unchanged (as compared with a pure gold solution
of the same concentration); in the presence of the gold,
the much less luminous gelatin particles could not be
recognized. With the fluid Augo the particles continu-
ously formed groups and then flew away from each other;
the somewhat large addition of gelatin (about one hun-
dred times as much as was necessary to produce a pro-
tective effect), appeared to oppose group formation, with-
out, however, destroying the free mobility of the gold
particles. Even subsequent addition of NaNOs altered
the microscopic appearance but little. Larger additions
of gelatin produced a further decrease in mobility, but
by no means destroyed it.
