Notes on “ Inclusions” in Gems, &e. By Isaac Lea, 199 
Cavities in quartz crystals enclosing fluids have been observed 
by the older mineralogists, but the kind of fluid, and gas or air, 
was not ascertained by them. Sir Humphry Davy, in 1822,* 
investigated the contents of these cavities, and found them generally 
pure water. The gas-bubbles were sometimes found to be “ azote.” 
Sir David Brewster, in 1823, + published a memoir of great research 
and value. He first had his attention called to the examination of 
fluid in cavities by the explosion of a crystal of topaz when heating 
it. He found cavities and air-bubbles in nearly twenty different 
substances, and these inclusions were carefully examined by him. 
In some of these cavities he observed two fluids { and crystals, and 
these are figured in his plates. Subsequently, Mr. Sorby pub- 
lished a long and admirable paper § on fluid cavities and crystals 
in minerals, with numerous and interesting figures. He con- 
sidered that the cubic crystals were probably chloride of sodium. 
In his investigation he proved, by forming artificial crystals, that, 
in a natural state, the fluid cavities, with their “ inclusions,” must 
have been formed by aqueo-igneous forces. He gives a figure of 
fluid in mica, but I have never seen any in that mineral, although 
many hundreds have passed under my microscope in looking after 
crystals of magnetite, &c. Mr. Sorby also published a paper on 
cavities in quartz in the ‘ Phil. Mag.’ vol. xv. p. 158; also with 
Mr. Butler in ‘ Proc. Roy. Soc. London,’ vol. xvu. p. 299. Kirkel 
on “ Microscopic Minerals,” Neues Jahrbuch, 1870, p. 80, mentions 
bubbles and cubic crystals in quartz. He found iron glance and 
fluid in Eleeolite = Nephelite. In emery, from Naxos, he found 
fluid in cavities. 
In 1872, || Mr. Sang published an account of water in cavities 
of calcite. 
Very recently, Professor Hartley, King’s College, London, has 
published a very able paper on the subject of the fluid in 
quartz, &c.4] He says that Simmler in 1858, offering an inter- 
pretation of Brewster's observations, concluded that the expansible 
liquid was carbon dioxide. Professor Hartley states that in many 
cases the liquid in quartz is water, but that in some cases he found 
the two fluids; and his very satisfactory and careful experiments 
show conclusively that the most volatile of the two fluids is car- 
bonic dioxide. He found in every experiment that the fiuid dis- 
appeared when exposed to 31° C., and reappeared on cooling. 
Professor Hartley accords with Mr. Sorby in his reasoning that 
* ¢Phil. Trans.’ 1822. 
+ ‘Trans. Roy. Soc. Edin.’ 1823. 
$ These two fluids Professor Dana without any analysis has called Brewster- 
linite and Cryptolinite. 
§ ‘Journ. Geol. Soe.’ vol. xiv., 1858, “‘ Micro-structure of Crystals,” 
|| ‘ Proc. Roy. Soc. Edin.’ p. 126. 
q ‘Journ, of the Chem, Soc. London,’ February 1876. 
