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 natm-al 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 

 lio-ht 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 quai-tz 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 Robert Were Fox,* in which he describes certain 

 pseudomorphous octohedrons of quartz, " more than an inch in diameter," which 

 " were broken fi'om a copper vein in Killas, 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 sahne 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 Cor;iwall, quoted in Edin. Phil. .Toui-nal, vol. xl., 

 p. 115. 



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