156 DR WILSON ON THE SOLUBILITY OF 
This fact, besides its interest in relation to natural history, will be welcome to 
chemists, as adding another link to the lengthened chain of analogies between 
chlorine, bromine, iodine, and fluorine. In teaching the beautiful law that bodies 
closely allied in chemical characters occur together in nature, I have always felt the 
force of the argument weakened, by the absence of fluorine from sea-water where 
the other members of its class are so abundant. Its detection in bittern removes 
the difficulty, and adds another to the many relations which are common to the 
well-marked natural family of simple-salt radicals to which it belongs. 
4. Of the presence of Fluorine in Minerals. 
It remains to connect the initial fact of this paper with the occurrence of 
fluorine in minerals, and in plants, and animals ; and, first, of minerals. I exclude, 
in the meanwhile from notice, fossil bones, which will be best considered in rela- 
tion to animal remains. 
The solvent power of water over fluoride of calcium is likely to throw some 
light both on the appearance and disappearance of that substance from particular 
localities, in relation to geological changes. In connection with this branch of 
our subject, Mr Rose has reminded me of a phenomenon familiar to mineralo- 
gists, namely, the frequent occurrence of quartz with deep cubical impressions on 
its surface, believed to be casts of crystals of fluor-spar, which had been dissolved 
away after the deposition of the silica. It is possible that the markings may 
have been occasioned by galena or iron pyrites, the latter of which we know, in 
contact with air, can change into sulphate of iron and sulphuric acid, and is then 
quite soluble in water, and might be readily carried away. Cubical iron pyrites, 
however, in general is quite permanent, and suffers no change even with the freest 
exposure to air; and galena is an exceedingly insoluble substance. Mineralogists, 
accordingly, have universally agreed that the square impressions on quartz are 
the imprints of fluor, and the very frequent association in nature of the latter 
with silica, seems to justify their view. It has been a problem, however, what 
agent has removed the fluor ; and it seems not impossible that water may have 
been the body which dissolved it away. In confirmation of this idea, I may 
refer to a paper by Mr Roperr Were Fox,* in which he describes certain 
pseudomorphous octohedrons of quartz, “ more than an inch in diameter,” which 
‘«‘ were broken from a copper vein in [z//as, at the depth of about 160 fathoms from 
the surface.” The crystals were hollow, and many of them contained, hermetically 
enclosed within them, water, or rather an aqueous saline solution, and numerous 
pieces of fluor. “Of these,” Mr Fox says, ‘all the fragments are corroded, and 
indicate, by their rounded edges and indented surfaces, the action of a solvent 
* Transactions of the Royal Polytechnic Society of Cornwall, quoted in Edin. Phil. Journal, vol. xl., 
p. 115. 
