184 MR. J. B. DANCER ON 



examine the chemical nature of the fluid, and the gas which 

 was sometimes contained in these cavities. 



He collected the fluid, in fine capillary tubes, from quartz 

 crystals obtained from various localities, and found that 

 in every case except one the fluid was water nearly pure ; 

 and in this single specimen it appeared to be naphtha, the 

 gas nitrogen, about 65 times as rare as the atmosphere. 

 In one cavity the gas, name not mentioned, was 10 times 

 as compressed as atmospheric air. 



In the naphtha-cavity there was almost a perfect vacuum. 



Mr. Sivright had previously found fluid in crystals of 

 calc-spar, sulphate of barytes, and sulphate of lime. 



Sir David Brewster discovered fluid-cavities in the 

 emerald, beryl, cymophane, and feldspar. He also found 

 fluid entangled in the following crystals, which were de- 

 posited from aqueous solutions : — Sulphates of iron, zinc, 

 copper, nickel, soda, magnesia, ammonia, magnesia and 

 iron, soda and magnesia, alumina and ammonia, and am- 

 monia and magnesia, nitrates of silver and strontium, oxalic 

 acid, tartrates of potash and soda. He next examined crys- 

 tals formed by heat and sublimation, but could not detect 

 a trace of any fluid ; this he considered highly favourable to 

 the aqueous origin of crystals containing water. In the 

 prosecution of this inquiry. Sir David Brewster employed 

 many ingenious experiments ; a detailed account of these 

 may be found in the ' Transactions of the Royal Society of 

 Edinburgh.' 



He discovered the existence of two new fluids in the 

 cavities of minerals, which are immiscible, and which pos- 

 sess remarkable physical properties ; Dana thus describes 

 them : — 



" One of these fluids has been named Brewstoline, after 

 its discoverer ; it is a liquid hydrocarbon, transparent and 

 colourless, and is nearly 32 times as expansible by heat as 

 water, increasing one-fourth of its volume by an increment 



