32 DR BREWSTEU on t/te Existence of Two New Fluids 



This class of cavities might, with propriety, have been divided 

 into three subdivisions : 1. Those where the cavities are entire- 

 ly filled with fluid ; 2. Those which have a perfect vacuum along 

 with the fluid ; and, 5. Those where the fluid is accompanied 

 with a gaseous body ; but, as several crystals seem to possess ca- 

 vities with all these characters, I shall describe the different 

 crystals in their order. 



1. AMETHYST from CEYLON. This fine specimen, in the ca- 

 binet of Mr THOMSON of Forth Street, originally belonged to 

 the King of Candy. It is about 3 inches long and If broad, 

 and has a large cavity, of the size and form shewn in Fig. 29- 

 The bubble V, which I have ascertained to be gaseous, by the 

 reflexion of light, moves by starts from one end of the cavity to 

 the other. It is not sensibly altered by heat. Another cavity 

 C, near the large one, has a small air-bubble in the middle, 

 which refuses to move from its place. There are several pieces 

 of opaque solid mater, which, with a little management, may be 

 seen within the cavity AB, and which may be made to fall from 

 one side of it to the other. This is the largest cavity that I have 

 ever seen in a solid crystal. 



2. ROCK CRYSTAL. This mineral abounds with cavities, con- 

 taining water and mineral oil, which is sometimes black, some- 

 times of a faint yellow, and sometimes of a rich orange red co- 

 lour. 



The largest cavities are generally amorphous ; but there are 

 many crystals with thousands of cavities all regularly crystallized, 

 and of the exact form of the secondary crystal. 



The quartz crystals from Quebec contain great quantities of 

 mineral oil, which does not perceptibly expand by the applica- 

 tion of heat. There are frequently within the cavities dark 

 little fragments, which are carried about by the motion of the 



