Dr Brewster on the New Fluid in Sapphire. ' 155 



M. Seetzen has given a similar account of Nakous, in Zach's 

 Ephemerides for October 1812. — See Daubeny's Description 

 of Active and Extinct Volcanoes. Lond. 1826. p. 437. 



Art. XXIV. — Notice respecting the existence of the New 

 Fluid in a large cavity in a specimen of Sapphire. By 

 David Brewster, LL. D. F. R. S. and Sec. R. S. Edin. 



In two papers which are printed in this Journal, I have fully 

 described the physical properties of the two new fluids which 

 occur in mineral bodies. These fluids having been found only 

 in the precious stones, — in quartz, amethyst, topaz, and chry- 

 soberyl, it became interesting to detect them in other minerals, 

 not only with the view of establishing their general prevalence 

 at the formation of this class of bodies, but of ascertaining if 

 they experienced any change in their properties from the mi- 

 neral in which they are found. 



Mr Sanderson lately put into my hands a specimen of sap- 

 phire, containing a very large fluid cavity, which, from the 

 expansible nature of the fluid, seemed to resemble that which 

 occurs in topaz. The cavity itself is regularly crystallized, 

 and is about one-third of an inch in length. The fluid occu- 

 pies about two-thirds of its length, and fills the cavity at a 

 temperature of 82° of Fahrenheit. It seems to be more viscid 

 and more dense than I have usually observed it, and in con- 

 sequence of this property, the capillary margin of the fluid re- 

 mains distinct and well marked, even at the instant when it 

 fills the cavity. When the temperature descends below 82°, 

 the contraction of the fluid is not accompanied with that vio- 

 lent effervescence which takes place in the deep cavities in 

 topaz. 



In the specimen under consideration, the fluid seems to have 

 exerted a high expansive force upon the sides of the cavity, 

 which it has succeeded in opening on both sides. The sur- 

 faces of the fissures thus occasioned, are covered with specks 

 of a gelatinous-looking matter, like portions of the second 

 fluid, when in a state of induration. The force, however, was 

 not sufficient to burst the specimen, and the only effect of it 

 seems to have been to expel into the fissures the second fluid, 

 which always occupies the angular and narrow parts of the 



