Fluids in the Cavities of Minerals. 219 
Sect: U.—On the co-existence of two immiscible fluids, of 
different physical properties, in the cavities of minerals, 
and accompanied with a vacuity. 
The phenomenon of two immiscible fluids, as exhibited in 
topaz, is represented in fig 5, where V is the vacuity, NN 
id, and WWW another fluid, which we shall dis- 
tinguish by the name of the second flued. ‘This second fluid 
WW commonly occupies the angles of triangular cavities, as 
in Fig. 5, or the terminations of longitudinal ones. _ It is al- 
ways separated from the new fluid by a curved surface mn, 
n, t never expands perceptibly with heat, and never 
mixes with the new fluid NN. a little management, the 
vacuity V may be made to come in contact with the bounding 
lines mn, mn, &c. ; but it never affects its curvature, and sel- 
dom enters the fluid W. When the vacuity V has been made 
to vanish by heat, these bounding lines remain exactly the 
same. 
Having at first observed this second fluid only in the angles. 
of cavities, as in Fig. 5, considerable difficulty was experien- 
ced in proving that it was a fluid. The difficulty of conceiv- 
on- 
DEF (shaded darkly.) The first portion A of the ‘new fluid 
Y, Z, while the other two portions 
branch, our author did not doubt that the vacuities of the 
portions B aud C had passed over the second fluid into the 
