34 DR BREWSTER on the Existence of Two New Fluids 



4. CYMOPHANE. In several specimens of cymophane, there 

 are strata of cavities apparently containing one fluid, but without 

 any perceptible vacuity. In the crystal containing the stratum 

 with the new fluids, there is another stratum parallel to it, of a 

 very remarkable kind, where the cavities have the form shewn 

 in Fig. 32. The nature of the fluid, however, I have not been 

 able to determine. 



5. PERIDOT. The largest and finest crystals of this mineral 

 are often intersected, in various directions, with strata of fluid 

 cavities having globules of air. In a set of unusually large crystals 

 a kind of resinous indurated matter seems to have been diffused, 

 sometimes in strata and sometimes throughout the mass of the 

 crystal. These peridots, which are very magnificent, belong to 

 the COUNTESS of WEMYSS ; but in consequence of their being 

 cut and set in gold, it was impossible to subject them to an ac- 

 curate examination. 



6. FELSPAR. The cavities in this mineral are very flat, and 

 irregularly formed. They contain a single fluid and an air-bub- 

 ble, which neither vanishes nor diminishes with heat. 



7. EMERALD and BERYL. The great degree of foulness 

 which is so common in these gems, arises generally from strata 

 of cavities containing a single fluid, and an air-bubble, which do 

 not perceptibly decrease with a temperature of 150. 



8 FLUOR-SPAR. The crystals of green fluor-spar from Als- 

 ton Moor frequently contain cavities with water. I have seen 

 several about half an inch long, and of the form of a triangular 

 pyramid. The air-bubble moves sluggishly even in these large 

 ones, and with great difficulty in the small ones. The apparent 

 air-bubble is gaseous, and the fluid does not perceptibly expand 



