22 Du BREWSTER on the Existence of Two New Fluids 



experiment with this crystal, one of the cavities burst, with a 

 heat not above 150, and the fracture round the cavity was co- 

 vered with specks of an inspissated fluid *. 



The formation of cavities with two fluids, and without any 

 vacuity, admits of an easy explanation, when they are connected 

 with other cavities, as in Figs. 15. 16., as there can be no doubt, 

 from the phenomena already described, that part of the fluid W 

 has passed through the narrow channel which connects the cavi- 

 ties. When the cavities, however, are entirely insulated, the ex- 

 planation is more difficult. 



SECT. IV. On the Changes which these Fluids have undergone in 



particular Crystals. 



In the absence of all information respecting the nature and 

 constitution of these fluids, it becomes interesting to ascertain, 

 whether time, or accidental causes, have produced any per- 

 ceptible changes in their physical properties. With this view, I 

 have examined an immense variety of specimens, and have been 

 led to results of considerable interest. 



In some specimens of topaz containing the two fluids, I have 

 observed several cavities in which the new fluid N is quite 

 opaque, as at a, Fig. 24., and others in which it has the appear- 

 ance shewn at b. 



There are some cavities, such as that shewn at c, where 

 the fluid seems to have left a crust, lining the interior of it, 

 and there are others where a sort of black farinaceous matter 

 appears, both within and around the cavities, that appear to 

 have been burst by some accidental cause. 



This crystal is the one referred to in page II. 



