180 JOURNAL OF THE [JUTie, 



sapphire, emerald, aquamarine, tourmaline, fiuorite, chrysoberyl, 

 and, above all, the topaz* and the amethyst. Many a micro- 

 scopist is unaware of the beautiful inclosures which are to be 

 found in the jewels in the possession of his own family, and 

 which can generally be examined even without removing the 

 gems from their setting, the jewels being merely held in the 

 stage-forceps under a low-power objective. To prevent inter- 

 ference by reflection from the many facets, a temporary mount 

 may be made by cementing to the gem a thin cover-glass with a 

 drop of thickened but cold balsam. After examination, the 

 balsam can be removed by immersion a short time in benzine or 

 spirits of turpentine. Many lapidaries and dealers are aware 

 that the flaws which occur in gems and greatly decrease their 

 value consist largely of inclosures ; — sometimes minute inclosed 

 crystals of other minerals ; sometimes cavities filled with some 

 gas and beautifully faceted with the crystalline form belonging 

 to the material of the gem ; sometimes cavities of a great varir' 

 of forms, filled partly or wholly with a liquid i'^ ' .,r ■ 



bubble of gas, and having, peTb" 

 gems or cubes of salt clinging to '• 



come when, as a matter of sciertii" ^ocss 



a gem will pride themselves .^icn it contains 



rather than on their absence — ai icast, so far as the flaws repre- 

 sent either included crystals or fluid-cavities. 



I shall invite your attention this evening to the subject of the 

 fluid-cavities in quartz, or rock-crystal, putting aside altogether 

 those contained in other minerals. 



The first point claiming consideration is the selection and 

 preparation of material. The material is plentiful in which 

 these cavities occur in forms of great variety and with fluid con- 

 tents of an exceedingly interesting character. The number of 

 localities at which such specimens have been found has increased 

 largely within the last few years, and it is probable that In a 

 short time any investigator of this subject will know where to 

 look for suitable material without leaving the place in which he 

 resides. It can be procured in abundance on the island of New 

 York from several sources ; viz., the quartz-grains in the common 



"Sir David Brewster. See, for ref., J. D. Dana's " System of Mineralogy," articles 

 Brewsterliuite and Cryptoliuite ; also Phil. Mag., 1847, (3), XXXI., p. 497 ; 1853, (4), V., p. 

 335; etc.— R Th. Simrnler : Pogg. Ann., 1858, CV., p. 400.-11. Vogelsang and H. Geissler : 

 Pogg. Ann., 1809, CXXXVIL, p. 50.— Alexis A. Julien : Jour. Am. Chem. Soc, III. 



